automate Helm reference updates

[dangrondahl]

Helm chart documentation should be updated automatically on new releases,
mirroring the existing `update-cli-docs.yml` workflow for CLI reference.

Tasks

• Identify what Helm reference content needs to be generated and from which source
• Create a workflow analogous to `.github/workflows/update-cli-docs.yml`
• Trigger on Helm chart releases (repository dispatch or workflow dispatch)
• Open a PR with the updated content automatically

References

• `.github/workflows/update-cli-docs.yml`