feat(helm): add generic command/args override and customConfigMap volume

[rzala]

• Add operator.command and operator.args for container command override
• Add operator.customConfigMap to mount inline or existing ConfigMap volumes
• Useful for wrapping the operator with custom entrypoint scripts

Checklist

• I've read the guidelines for contributing to this repository.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

[rzala]

this PR touches the same areas in deployment.yaml and values.yaml as #2888 (extraContainers/extraVolumes). If both end up getting merged, whichever goes in second will have a merge conflict in the volumeMounts and volumes sections. Nothing major, just needs the if conditions and blocks from both PRs combined. Happy to rebase once the other one lands if that helps.