fix: Add filtering for Lease metrics

[ntoofu]

What this PR does / why we need it:

Lease metrics are filtered by namespaces when --namespaces or --namespaces-denylist is specified.

How does this change affect the cardinality of KSM: (increases, decreases or does not change cardinality)

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 #2121

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[ntoofu]

I tried to write test which ensures that --namespace filters lease resources, but other resources such as configmap seem to have no equivalent test. Should I write test only for lease, or no such test is required?

[mrueg]

Thanks for your contribution @ntoofu
Changes look good, additional tests would be welcome. Feel free to add them in a follow-up PR!

/lgtm

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mrueg, ntoofu

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