[WIP] fix: Add allowed labels to all metrics instead of just _labels metric

[ronaknnathani]

What this PR does / why we need it:
KSM allows providing a list of labels that should be added to the prometheus metric for the resource. These labels currently are only added to the kube_<resource>_labels metric. However, there are several use cases where having these labels on all of the metrics for the resource would be helpful. This change adds the allowed labels to all metrics of the resource instead of just the _labels metric.

Note

Currently, I have only made the change for Pod metrics. If this direction looks good, I can update the PR for rest of the resources.

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)
Doesn't change the number of metrics.
Increases the labels on each prometheus metric based on allowed labels.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):

Fixes #2311

Tests
Tested locally against a kind cluster. Just showing a handful of metrics here.

kube_pod_container_info{namespace="kube-system",pod="kindnet-l4529",uid="5e107535-3135-48fb-8f42-043c50866177",container="kindnet-cni",image_spec="docker.io/kindest/kindnetd:v20230511-dc714da8",image="docker.io/kindest/kindnetd:v20230511-dc714da8",image_id="sha256:b18bf71b941bae2e12db1c07e567ad14e4febbc778310a0fc64487f1ac877d79",container_id="containerd://d37637e9cfc42cb4f9f606de57d5ced7fb242827e2b4d8860e6c3a28ca877136",label_app="kindnet"} 1
kube_pod_container_info{namespace="monitoring",pod="event-exporter-7ddc6ff9b-wd8f5",uid="a021852f-75f6-4e1c-975a-103396730b68",container="event-exporter",image_spec="kubernetes-event-exporter:local",image="docker.io/library/kubernetes-event-exporter:local",image_id="docker.io/library/import-2024-01-17@sha256:73a75a4829b55788efebd1ac7679256c36a09216c0384363716c3ae22e5fba5b",container_id="containerd://a8643a9cf05a6e7d708cd685822fc3799ba45655f58c5d30930cd21e545f8a22",label_app="event-exporter"} 1
...
kube_pod_container_resource_limits{namespace="rnathani",pod="web-server-869d57bbd4-vljdh",uid="085c44c5-b992-4525-a92c-266d32bfeaa6",container="web-server",node="kind-control-plane",resource="memory",unit="byte",label_app="web-server"} 1.073741824e+09
kube_pod_container_resource_limits{namespace="kube-system",pod="kindnet-l4529",uid="5e107535-3135-48fb-8f42-043c50866177",container="kindnet-cni",node="kind-control-plane",resource="cpu",unit="core",label_app="kindnet"} 0.1
...
kube_pod_container_state_started{namespace="monitoring",pod="event-exporter-7ddc6ff9b-s6zfg",uid="fe1e9f75-3118-43cf-b48c-1ac347152a6b",container="event-exporter",label_app="event-exporter"} 1.716671651e+09
kube_pod_container_state_started{namespace="local-path-storage",pod="local-path-provisioner-6f8956fb48-sv66c",uid="33ebe75c-56be-4208-bf3b-7e1d9546738b",container="local-path-provisioner",label_app="local-path-provisioner"} 1.716671697e+09
...
kube_pod_container_status_ready{namespace="rnathani",pod="web-server-869d57bbd4-vljdh",uid="085c44c5-b992-4525-a92c-266d32bfeaa6",container="web-server",label_app="web-server"} 1
kube_pod_container_status_ready{namespace="kube-system",pod="kindnet-l4529",uid="5e107535-3135-48fb-8f42-043c50866177",container="kindnet-cni",label_app="kindnet"} 1
...

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[ronaknnathani]

@mrueg @CatherineF-dev - just checking if you got a chance to take a look. if this direction is okay, I can update the PR for rest of the resources or also send different PRs for different resources.

[mrueg]

I don't think this is a good idea to add all labels to all metrics as the cardinality will go up by a lot.
Instead you should join the _labels metric into the metric you want identified by the keys. Usually you can do this either per query you run or if you have a specific need use a recording rule.

/hold