Enable pod and container securityContext customization

[daniil-nedostup]

Is your feature request related to a problem? Please describe.
It is currently not possible to override securityContext values for the codebase-operator Deployment. This limitation makes it harder to comply with security policies that require custom runAsUser, fsGroup, or container-level settings like readOnlyRootFilesystem.

Describe the solution you'd like
Add support for overriding both podSecurityContext and containerSecurityContext via Helm values, so users can define custom security settings at the pod and container levels.

Describe alternatives you've considered
An alternative is to manually patch the Deployment after installation, but this approach is not sustainable and conflicts with GitOps workflows or Helm-based automation.

Additional context
This enhancement would align the codebase-operator chart with best practices and provide better flexibility for platform and security teams. Similar configuration patterns are already used in other Helm charts across the platform.