feat: use indexer to retrieve endpointslices directly by service name

[defaulterrr]

What this PR does / why we need it:

Why is this change required? What problem does it solve?

This contribution increases overall performance of the sync portion in the controller for clusters with large amounts of services and endpointslices. Previously, for each service controller would list all endpointslices in it's storer (which may contain thousands of objects) and filter them using some string magic that is based on the internals of how endpointslice controller works on the control plane side. This is bad in both terms of performance and future-proofness:

• Having 10000 services and 10000 endpointslices in cluster will result in processing of about 100_000_000 strings. Using indexed storage allows controller to get required slices with O(1) time complexity
• Relying on how endpointslice controller generates names creates an implicit dependency on the control-plane-specific mechanisms. K8s already provides a much easier way to connect endpointslices to their parent services. As this ingress controller relies on services to be present (as in we don't process endpointslices created manually), i see no reason not to just use this built-in label

Also, while fixing the failing tests, i've found that some of the tests were logically incorrect - as in they were not matching slices that were owned by requested service.

What i've done

1. Created a new indexer named after a tech-label "kubernetes.io/service-name"
2. Added this indexer to the existing informer to index all incoming objects
3. Used this index in ByKey function of the lister and removed previous code which filtered eps using string magic
4. Fixed tests that were covering this functionality and introduced indexer to their setup

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• CVE Report (Scanner found CVE and adding report)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation only

How Has This Been Tested?

This change alters the internal behaviour of the controller, but does not affect user-facing behaviours, so no new tests are required in my opinion. I've updated & fixed tests that were covering this section of the code. As i've changed one of the test cases "the key exists" i'd like to confirm that following is the expected behaviour: MatchByKey function will return all endpointslices that were created by the provided service key, as in were created and are in the same namespace as this service. Previous test case was not matching this condition as one of the endpointslices created by the same service was not returned (and so ingress-controller would not pass it's endpoints to the nginx).

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I've read the CONTRIBUTION guide
• I have added unit and/or e2e tests to cover my changes.
• All new and existing tests passed.

[linux-foundation-easycla]

• ✅login: defaulterrr / (dff0055)

The committers listed above are authorized under a signed CLA.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: defaulterrr
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[k8s-ci-robot]

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✅ Deploy Preview for kubernetes-ingress-nginx canceled.

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[Gacko]

/uncc

[Gacko]

/cc @strongjz @tao12345666333 @cpanato

[strongjz]

/kind feature
/ok-to-test
/priority backlog
/triage accepted