Add option to skip older k8s events

[ChrsMark]

What does this PR do?

This PR adds option to skip older k8s events in event metricset of kubernetes module.

Why is it important?

There might be cases that LastTimestamp

beats/metricbeat/module/kubernetes/event/event.go

Lines 107 to 112 in a350c32

	// skip events happened before watch
	FilterFunc: func(obj interface{}) bool {
	eve := obj.(*kubernetes.Event)
	if kubernetes.Time(&eve.LastTimestamp).Before(now) {
	return false
	}

is not populated properly (either buggy situation or updated API) and this results into all events being dropped. We need an option here to make the filtering configurable and avoid having Metricbeat dropping all events in case the LastTimestamp is not set.

Related to #28923

[mergify]

This pull request does not have a backport label. Could you fix it @ChrsMark? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 7./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[elasticmachine]

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Build stats

• Start Time: 2021-12-14T12:12:00.453+0000

• Duration: 87 min 17 sec

• Commit: a09571d

Test stats 🧪

Test	Results
Failed	0
Passed	9356
Skipped	2421
Total	11777

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[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b add_option_to_skip_events_k8s upstream/add_option_to_skip_events_k8s
git merge upstream/master
git push upstream add_option_to_skip_events_k8s

[MichaelKatsoulis]

This value should come from the config like skipOlder: config.SkipOlder.
Now it is hardcoded to true.

[ChrsMark]

🤦🏼‍♂️ you are right! Thanks for catching this!

[MichaelKatsoulis]

LGTM