[Draft] Validation Webhook for splunk-operator

[patrykw-splunk]

Description

This PR aims to add validation webhook for splunk-operator. This includes every CRD that operator consist of.

Key Changes

[DRAFT]

• Dummy validation webhook implementation
• Kustomize config
• cert-manager config

Testing and Verification

N/A

Related Issues

N/A

PR Checklist

• Code changes adhere to the project's coding standards.
• Relevant unit and integration tests are included.
• Documentation has been updated accordingly.
• All tests pass locally.
• The PR description follows the project's guidelines.

[coveralls]

Pull Request Test Coverage Report for Build 21135429752

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.008%) to 86.363%

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Files with Coverage Reduction	New Missed Lines	%
pkg/splunk/enterprise/cp.go	1	33.33%

Totals
Change from base Build 21029015253:	-0.008%
Covered Lines:	10728
Relevant Lines:	12422

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💛 - Coveralls

[kasiakoziol]

I think it requires updating to 2026 included

[kasiakoziol]

We don't need an error return at all if we always return nil

[kasiakoziol]

And if we always return nil in SetupWebhookWithManager, then this if is not required