Cherry-pick #24788 to 7.x: Expose processes and their metrics

[michalpristas]

Cherry-pick of PR #24788 to 7.x branch. Original message:

What does this PR do?

Added /processes and /processes/{processID} endpoints to http server.

agent has its server on unix:///tmp/elastic-agent/elastic-agent.sock or npipe:///elastic-agent for windows.
not configurable

example of /processes

{
	"processes": [{
		"id": "filebeat-default-monitoring",
		"pid": "8025",
		"binary": "filebeat",
		"source": {
			"kind": "internal",
			"outputs": ["default"]
		}
	}, {
		"id": "metricbeat-default-monitoring",
		"pid": "8043",
		"binary": "metricbeat",
		"source": {
			"kind": "internal",
			"outputs": ["default"]
		}
	}, {
		"id": "metricbeat-default",
		"pid": "7998",
		"binary": "metricbeat",
		"source": {
			"kind": "configured",
			"outputs": ["default"]
		}
	}]
}

example of /processes/metricbeat-default

{
	"beat": {
		"cgroup": {
			"cpu": {
				"cfs": {
					"period": {
						"us": 100000
					},
					"quota": {
						"us": 0
					}
				},
				"id": "user.slice",
				"stats": {
					"periods": 0,
					"throttled": {
						"ns": 0,
						"periods": 0
					}
				}
			},
			"cpuacct": {
				"id": "user.slice",
				"total": {
					"ns": 994162833024
				}
			},
			"memory": {
				"id": "user.slice",
				"mem": {
					"limit": {
						"bytes": 9223372036854771712
					},
					"usage": {
						"bytes": 1766760448
					}
				}
			}
		},
		"cpu": {
			"system": {
				"ticks": 150,
				"time": {
					"ms": 156
				}
			},
			"total": {
				"ticks": 220,
				"time": {
					"ms": 232
				},
				"value": 220
			},
			"user": {
				"ticks": 70,
				"time": {
					"ms": 76
				}
			}
		},
		"handles": {
			"limit": {
				"hard": 1048576,
				"soft": 1024
			},
			"open": 17
		},
		"info": {
			"ephemeral_id": "aad52edf-4229-4927-bb30-c67ce9934499",
			"uptime": {
				"ms": 26728
			}
		},
		"memstats": {
			"gc_next": 16893216,
			"memory_alloc": 14370808,
			"memory_sys": 75056128,
			"memory_total": 34212120,
			"rss": 85266432
		},
		"runtime": {
			"goroutines": 58
		}
	},
	"libbeat": {
		"config": {
			"module": {
				"running": 4,
				"starts": 4,
				"stops": 0
			},
			"reloads": 1,
			"scans": 1
		},
		"output": {
			"events": {
				"acked": 0,
				"active": 0,
				"batches": 0,
				"dropped": 0,
				"duplicates": 0,
				"failed": 0,
				"toomany": 0,
				"total": 0
			},
			"read": {
				"bytes": 0,
				"errors": 0
			},
			"type": "elasticsearch",
			"write": {
				"bytes": 0,
				"errors": 0
			}
		},
		"pipeline": {
			"clients": 4,
			"events": {
				"active": 35,
				"dropped": 0,
				"failed": 0,
				"filtered": 0,
				"published": 35,
				"retry": 44,
				"total": 35
			},
			"queue": {
				"acked": 0
			}
		}
	},
	"metricbeat": {
		"system": {
			"cpu": {
				"events": 3,
				"failures": 0,
				"success": 3
			},
			"filesystem": {
				"events": 12,
				"failures": 0,
				"success": 12
			},
			"memory": {
				"events": 3,
				"failures": 0,
				"success": 3
			},
			"network": {
				"events": 17,
				"failures": 0,
				"success": 17
			}
		}
	},
	"system": {
		"cpu": {
			"cores": 4
		},
		"load": {
			"1": 0.58,
			"15": 1.43,
			"5": 1.43,
			"norm": {
				"1": 0.145,
				"15": 0.3575,
				"5": 0.3575
			}
		}
	}
}

in case of error e.g

{
	"type": "UNEXPECTED",
	"reason": "failed fetching metrics: Get \"http://unix/stats\": dial unix /tmp/elastic-agent/default/metricbeat/metricbeat.sock: connect: no such file or directory"
}

Why is it important?

Fixes: #24091

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

[elasticmachine]

Pinging @elastic/agent (Team:Agent)

[elasticmachine]

Pinging @elastic/ingest-management (Team:Ingest Management)

[elasticmachine]

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• Build Cause: Pull request #25017 updated

• Start Time: 2021-04-14T06:36:17.332+0000

• Duration: 146 min 23 sec

• Commit: 275012f

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Test	Results
Failed	0
Passed	46675
Skipped	5175
Total	51850

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Passed	46675
Skipped	5175
Total	51850

[simitt]

Is there anything blocking from merging this backport?

[michalpristas]

i dont see a green test, nothing aside from that