[processor/k8sattributes] introduce new observability metric otelcol.k8s.pod.association

[odubajDT]

Description

Introduction of new observability metric:

otelcol.k8s.pod.association

with status, otelcol.signal and pod_identifier attributes

Link to tracking issue

Related to #44587

[github-actions]

This PR was marked stale due to lack of activity. It will be closed in 14 days.

[ChrsMark]

I would be fine with adding the new metric following the suggested dots approach. However I think we should not close #44587 until we fixed the components' internal metrics according to open-telemetry/opentelemetry-collector#12909. WDYT?

[ChrsMark]

We briefly discussed this specific case during the Collector Stability SIG. We can wait to have open-telemetry/opentelemetry-collector#14273 merged and then we can try to migrate the internal metrics from _ to . through a component specific feature gates pair (following the pattern from open-telemetry/opentelemetry-collector#14273).

[mx-psi]

open-telemetry/opentelemetry-collector/pull/14273 is on the merge queue :)

[ChrsMark]

The addition LGTM (needs rebase).

But let's also ensure we do the rename (_ to using .) as part of the related issue: #44718 (comment)