feat: new release process

[emaydeck-mozilla]

The previous release process ran chart version checks and helm-docs generation as pre-commit hooks, requiring contributors to manually bump versions and regenerate docs before a commit could go through. PRs with multiple commits have usually forced contributors into scenarios where they must choose to either continually bump chart versions or skip pre-commit checks altogether, neither of which is ideal. Additionally, with more contributors regularly working in this repo, requiring users to manage chart versions as part of their changes has created merge conflicts that have become increasingly cumbersome to work around.

This PR moves version bumping and helm-docs updates into CI, where they happen automatically at merge time based on a PR label. This follows a pattern already in use in the terraform-modules repo, where the title of the PR is used to programmatically determine the change level (major/minor/patch) if semantic commit messages are used. Users may also manually label PRs to set or override the change level.

The pre-commit hook that checked for version bumps has been removed, and contributors no longer need to think about versioning as part of their local commit flow.

Changes:

• Removed the chartkit-version-check pre-commit hook; version bumps are now handled by CI on merge
• Deleted auto-push-tag-helm-charts.yaml and replaced it with two new workflows and two composite actions:
  • pr-chart-management.yaml detects changed charts, infers a release label from the PR title (conventional commit format), posts a version bump preview comment, and runs the full
    release on merge
  • manually-release-helm-charts.yaml provides a workflow_dispatch for bumping and publishing without a PR
  • bump-and-commit composite action bumps chart versions (with cascade), regenerates helm-docs, and commits back to main
  • package-and-push composite action packages and pushes charts to the OCI registry and creates git tags
• Fixed no-release label acting as lowest-priority severity rather than a veto; it now always wins regardless of what other labels are present
• Updated chartkit version bump CLI: renamed --part to --release-type, replaced --json flag with a --format option supporting text, json, and markdown output; JSON output now includes
  previous_version and path fields needed by the release workflow
• Updated CONTRIBUTING.md and README.md to document the new release process, including label inference rules, override instructions, the one-release-type-per-PR limitation, and the
  manual workflow dispatch
• Fixed stale --part reference in scripts/README.md

[grahamalama]

I'm not sure if this is still needed these days, but https://github.com/orgs/community/discussions/26560#discussioncomment-3531273

git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
git config user.name "github-actions[bot]"