[chore] [receiver/k8sobjects] Extract logic for watching/pulling K8s resources into separate package

[bacherfl]

Description

This PR refactors the k8sobjects receiver by extracting the components responsible for receiving the K8s resources in the cluster into a separate package with an Observer interface, and the pull/watch based implementations thereof.
This package can then also be used by the k8sevents receiver, which would then only need to format the received events to conform with the semantic conventions.

Link to tracking issue

Part of #40825 - next steps as part of this issue would be to also make use of the observer components in the k8seventsreceiver

Testing

Added tests for the new components. The tests for the receiver itself could be refactored to not use the concrete implementations of the Observer interface, but that should probably be done as a follow up to not make this PR too large

[ChrsMark]

Thank's for working on this!
Overall looks good with some nits.

[bacherfl]

Thank's for working on this! Overall looks good with some nits.

Thanks for the feedback @ChrsMark! I will address the comments and update the PR in the next few days

[krisztianfekete]

In the current code, watchers have their own copy of the config:

opentelemetry-collector-contrib/receiver/k8sobjectsreceiver/receiver.go

Lines 288 to 310 in 21380a7

	cancelCtx, cancel := context.WithCancel(ctx)
	defer cancel()
	cfgCopy := *config
	wait.UntilWithContext(cancelCtx, func(newCtx context.Context) {
	resourceVersion, err := getResourceVersion(newCtx, &cfgCopy, resource)
	if err != nil {
	kr.setting.Logger.Error("could not retrieve a resourceVersion",
	zap.String("resource", cfgCopy.gvr.String()),
	zap.Error(err))
	cancel()
	return
	}
	done := kr.doWatch(newCtx, &cfgCopy, resourceVersion, watchFunc, stopperChan)
	if done {
	cancel()
	return
	}
	// need to restart with a fresh resource version
	cfgCopy.ResourceVersion = ""
	}, 0)
	}

while here, config seems to be shared, so all goroutines will operate on the same ResourceVersion, right?

[bacherfl]

There would be one instance of an Observer per resource type, where each one has its own copy of the config, so they should not use the same resource version. An example of how this would be used in the k8sobjectsreceiver can be seen in the following commit: 553fc36#diff-50ed6c76b6431c811210dccb90da133a8ef78e9321de67aceb801301b21ad723L110-L138 - I had to undo this change for this PR because the introduction of the new module and the adaptation of the k8sobserver to use the new module has to be done in two separate PRs

[atoulme]

@hvaghani221, @TylerHelmuth, @ChrsMark, @krisztianfekete please review as codeowners?

[ChrsMark]

3/5 code-owners approved and Tyler is out this week. I think we can merge this since it's an internal package addition and the actual refactoring will come as follow-up.