Add ability to disable namespace opt-in

[slimm609]

Description of the change

• add the ability to disable opt-in support for namespace validation and enforce across the entire cluster
• add helm-docs template to allow helm-docs to generate the README automatically.

Existing or Associated Issue(s)

https://github.com/sigstore/policy-controller/issues/66

Additional Information

Checklist

• [X] Chart version bumped in Chart.yaml according to semver. Where applicable, update and bump the versions in any associated umbrella chart
• [X] Variables are documented in the values.yaml and added to the README.md. THe helm-docs utility can be used to generate the necessary content. Use helm-docs --dry-run to preview the content
• [X] JSON Schema generated
• [X] List tests pass for Chart using the Chart Testing tool and the ct lint command

[hectorj2f]

@slimm609 Sorry, could you rebase these changes again ? I think this PR got lost somehow. Happy to help you to get it in.

[slimm609]

@hectorj2f rebased

[hectorj2f]

@slimm609 Could we remove the helm docs addition as part of this PR? We want to evaluate it's benefits in a separate PR.

[shani-e]

@hectorj2f @slimm609 Any chance to promote it? 🥺