Add restrictive security context to registry pod and init containers

[kaovilai]

Fixes #7039

Signed-off-by: Tiger Kaovilai passawit.kaovilai@gmail.com

Description of the change:

Motivation for the change:

Checklist

If the pull request includes user-facing changes, extra documentation is required:

• Add a new changelog fragment in changelog/fragments (see changelog/fragments/00-template.yaml)
• Add or update relevant sections of the docs website in website/content/en/docs

[Copilot]

Pull request overview

This PR enhances security by applying restrictive security contexts to init containers in the FBC registry pod, addressing issue #7039. Previously, only the main container received the restrictive security context when the --security-context-config=restricted flag was used.

Changes:

• Refactored security context creation into a reusable variable
• Added security context application to all init containers in the FBC registry pod

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[Copilot]

The new functionality that applies the restrictive security context to init containers lacks test coverage. The test file fbc_registry_pod_test.go has comprehensive tests for other functionality but does not verify that init containers receive the security context when SecurityContext is set to 'restricted'. Consider adding a test case that creates an FBCRegistryPod with SecurityContext: 'restricted' and verifies that both the main container and init containers have the expected security context settings.