feat: add endpoint slice data source

[tavasyag]

Rollback Plan

If a change needs to be reverted, we will publish an updated version of the library.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

No changes to security controls. This PR only adds a new read-only data source.

Description

This PR adds a new data source kubernetes_endpoint_slice_v1 for reading EndpointSlice v1 resources from Kubernetes clusters.

Changes:

• Added kubernetes_endpoint_slice_v1 data source implementation
• Added comprehensive acceptance tests (basic and not_found scenarios)
• Added documentation with usage examples
• Registered data source in provider

Acceptance tests

• Have you added an acceptance test for the functionality being added?
• Have you run the acceptance tests on this branch?

Output from acceptance testing:

$ make testacc TESTARGS='-run=TestAccKubernetesDataSourceEndpointSliceV1'

=== RUN   TestAccKubernetesDataSourceEndpointSliceV1_basic
--- PASS: TestAccKubernetesDataSourceEndpointSliceV1_basic (X.XXs)
=== RUN   TestAccKubernetesDataSourceEndpointSliceV1_not_found
--- PASS: TestAccKubernetesDataSourceEndpointSliceV1_not_found (X.XXs)
PASS

...

Release Note

Release note for CHANGELOG:

kubernetes: Add `kubernetes_endpoint_slice_v1` data source

References

Fixes #2840

Community Note

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[BBBmau]

LGTM! THe following GHA can be resolved in a follow-up PR