update validating webhook docs

[patrykw-splunk]

Description

This PR updates validation webhook documentation with steps for custom certificates setup

Key Changes

updated docs

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.

[github-actions]

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[kubabuczak]

Can we also provide helm-based installation path?