Add Agent example input autodiscover config for standalone k8s

[ChrsMark]

What does this PR do?

This PR is a follow up of #23938 to add a commented out section within the k8s manifest as an example for enabling autodiscover for specific target based on dynamic inputs and k8s provider.

It comes along with elastic/observability-docs#401.

Part of #23613

Why is it important?

So as to provide an easy way for the users to define their own autodiscover condition based inputs.

How to test this PR locally

1. Uncoment the added section
2. Deploy Agent on k8s: kubectl apply -f elastic-agent-standalone-kubernetes.yml
3. Deploy a target Redis Pod:

apiVersion: v1
kind: Service
metadata:
  name: redis
  labels:
    app: redis
spec:
  clusterIP: None
  ports:
  - name: web
    port: 6379
    protocol: TCP
  selector:
    app: redis
  type: ClusterIP
---
apiVersion: v1
kind: Pod
metadata:
  name: redis
  labels:
    role: main
    app: redis
spec:
  containers:
    - name: redis
      image: redis

4. Verify that redis integration start collecting redis metrics from the Pod. In Kibana discover filter on redis.info for event.dataset and expect to events arriving looking like the one below inScreenshots part.

Screenshots

Sample event:

{
  "_index": ".ds-metrics-redis.info-default-2021.02.22-000001",
  "_type": "_doc",
  "_id": "m_cZyncB1P74KB3B7J-v",
  "_version": 1,
  "_score": null,
  "_source": {
    "@timestamp": "2021-02-22T14:16:55.832Z",
    "service": {
      "version": "6.0.10",
      "address": "redis://10.244.1.8:6379",
      "type": "redis"
    },
    "os": {
      "full": "Linux 4.9.184-linuxkit x86_64"
    },
    "redis": {
      "info": {
        "stats": {
          "latest_fork_usec": 0,
          "keyspace": {
            "hits": 0,
            "misses": 0
          },
          "active_defrag": {
            "key_hits": 0,
            "key_misses": 0,
            "hits": 0,
            "misses": 0
          },
          "pubsub": {
            "patterns": 0,
            "channels": 0
          },
          "connections": {
            "received": 1,
            "rejected": 0
          },
          "keys": {
            "expired": 0,
            "evicted": 0
          },
          "commands_processed": 18,
          "sync": {
            "full": 0,
            "partial": {
              "err": 0,
              "ok": 0
            }
          },
          "instantaneous": {
            "input_kbps": 0,
            "output_kbps": 0,
            "ops_per_sec": 0
          },
          "migrate_cached_sockets": 0,
          "slave_expires_tracked_keys": 0,
          "net": {
            "input": {
              "bytes": 504
            },
            "output": {
              "bytes": 32651
            }
          }
        },
        "cluster": {
          "enabled": false
        },
        "clients": {
          "blocked": 0,
          "connected": 1,
          "longest_output_list": 0,
          "biggest_input_buf": 8,
          "max_output_buffer": 0,
          "max_input_buffer": 8
        },
        "persistence": {
          "loading": false,
          "rdb": {
            "bgsave": {
              "in_progress": false,
              "last_time": {
                "sec": -1
              },
              "current_time": {
                "sec": -1
              },
              "last_status": "ok"
            },
            "copy_on_write": {
              "last_size": 0
            },
            "last_save": {
              "changes_since": 0,
              "time": 1614003324
            }
          },
          "aof": {
            "fsync": {},
            "enabled": false,
            "rewrite": {
              "last_time": {
                "sec": -1
              },
              "current_time": {
                "sec": -1
              },
              "buffer": {},
              "in_progress": false,
              "scheduled": false
            },
            "bgrewrite": {
              "last_status": "ok"
            },
            "write": {
              "last_status": "ok"
            },
            "copy_on_write": {
              "last_size": 0
            },
            "buffer": {},
            "size": {}
          }
        },
        "replication": {
          "slave": {},
          "role": "master",
          "connected_slaves": 0,
          "master_offset": 0,
          "backlog": {
            "size": 1048576,
            "first_byte_offset": 0,
            "histlen": 0,
            "active": 0
          },
          "master": {
            "sync": {},
            "offset": 0,
            "second_offset": -1
          }
        },
        "memory": {
          "max": {
            "value": 0,
            "policy": "noeviction"
          },
          "fragmentation": {
            "ratio": 9.53,
            "bytes": 7031992
          },
          "active_defrag": {
            "is_running": false
          },
          "allocator": "jemalloc-5.1.0",
          "allocator_stats": {
            "allocated": 1135544,
            "active": 1355776,
            "resident": 4169728,
            "fragmentation": {
              "ratio": 1.19,
              "bytes": 220232
            },
            "rss": {
              "bytes": 2813952,
              "ratio": 3.08
            }
          },
          "used": {
            "rss": 7856128,
            "peak": 866680,
            "lua": 37888,
            "dataset": 43008,
            "value": 866680
          }
        },
        "cpu": {
          "used": {
            "sys_children": 0,
            "user_children": 0,
            "sys": 0.07,
            "user": 0.07
          }
        },
        "server": {
          "mode": "standalone",
          "run_id": "fa112bef9093d2ac5ccff855be0ae270375ad0f6",
          "lru_clock": 3390679,
          "hz": 10,
          "gcc_version": "8.3.0",
          "build_id": "1c3aed2f9fd88f03",
          "config_file": "",
          "git_dirty": "0",
          "uptime": 91,
          "tcp_port": 6379,
          "arch_bits": "64",
          "multiplexing_api": "epoll",
          "git_sha1": "00000000"
        },
        "slowlog": {
          "count": 0
        }
      }
    },
    "data_stream": {
      "type": "metrics",
      "dataset": "redis.info",
      "namespace": "default"
    },
    "elastic_agent": {
      "id": "9392caf0-cdfc-4abf-981b-f98cb6b9edad",
      "snapshot": true,
      "version": "8.0.0"
    },
    "host": {
      "hostname": "kind-worker",
      "architecture": "x86_64",
      "os": {
        "family": "redhat",
        "name": "CentOS Linux",
        "kernel": "4.9.184-linuxkit",
        "codename": "Core",
        "platform": "centos",
        "version": "7 (Core)"
      },
      "id": "17af4efd6a5716fb64a196f3cd53c4f8",
      "containerized": true,
      "name": "kind-worker",
      "ip": [
        "10.244.1.1",
        "10.244.1.1",
        "10.244.1.1",
        "172.18.0.2",
        "fc00:f853:ccd:e793::2",
        "fe80::42:acff:fe12:2"
      ],
      "mac": [
        "ba:4a:a1:a2:9a:81",
        "9a:80:f1:73:34:7a",
        "2e:0a:1c:40:46:f8",
        "02:42:ac:12:00:02"
      ]
    },
    "process": {
      "pid": 1
    },
    "event": {
      "module": "redis",
      "duration": 666897,
      "dataset": "redis.info"
    },
    "metricset": {
      "name": "info",
      "period": 10000
    },
    "kubernetes": {
      "namespace": "default",
      "pod": {
        "labels": {
          "role": "main",
          "app": "redis"
        },
        "name": "redis",
        "uid": "150148b5-b0a0-4237-b1ea-b2c2634fba59",
        "ip": "10.244.1.8"
      }
    },
    "agent": {
      "ephemeral_id": "7b49f72c-73c2-49be-99c9-b09d55fcd7b9",
      "id": "22e06d3f-a7cb-464c-b813-dee4302ca78a",
      "name": "kind-worker",
      "type": "metricbeat",
      "version": "8.0.0"
    },
    "ecs": {
      "version": "1.7.0"
    }
  },
  "fields": {
    "@timestamp": [
      "2021-02-22T14:16:55.832Z"
    ]
  },
  "highlight": {
    "event.dataset": [
      "@kibana-highlighted-field@redis.info@/kibana-highlighted-field@"
    ]
  },
  "sort": [
    1614003415832
  ]
}

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[elasticmachine]

Pinging @elastic/agent (Team:Agent)

[elasticmachine]

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• Build Cause: Pull request #24157 opened

• Start Time: 2021-02-22T14:32:11.177+0000

• Duration: 53 min 54 sec

• Commit: b828ce8

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