Adds unit tests to the subscriber/pkg/k8s package to cover core logic.

• Tests the 'addCustomLabels' utility function.
• Tests the 'applyRequest' function for both 'get' and 'create' operations using a fake dynamic client.

Resolves: #4914

Proposed changes

This PR adds unit tests to the subscriber/pkg/k8s package to satisfy issue #4914.

The new tests in operations_test.go cover:

• The addCustomLabels utility function.
• The applyRequest function for both "get" and "create" operations, using a fake.NewSimpleDynamicClient to mock the Kubernetes API interaction.

Types of changes

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• New feature (non-breaking change which adds functionality)
• Bugfix (non-breaking change which fixes an issue)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices applies)

Checklist

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• I have read the CONTRIBUTING doc
• I have signed the commit for DCO to be passed.
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if appropriate)
• I have added necessary documentation (if appropriate)

Dependency

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