docs: clarify release checklist branch

[Zakharden]

Summary

Update the maintainer release checklist so the branch used for major/minor release work is explicit instead of being hardcoded to main.

The checklist now defines DEVELOPMENT_BRANCH, keeps main as the default for Helm 4 and later releases, and documents dev-v3 for Helm 3 release work.

Fixes #1917.

Validation

• corepack yarn install --frozen-lockfile
• corepack yarn build
• git diff --check HEAD~1 HEAD
• rg -n "from main|off main|cherry-picking from main|git checkout main|upstream/main|DEVELOPMENT_BRANCH|dev-v3" community/release_checklist.md

[Zakharden]

This PR is still blocked by workflow/action state. I can rebase/update if needed, but right now only maintainer/CI rerun is needed. Please ping me if you want me to push a trivial follow-up.

[Zakharden]

Thanks, maintainer-side checks are the only blocker here. No code changes were made from my side.

Please rerun the remaining action-required CI when possible so we can confirm readiness for merge.

[Zakharden]

I’ve finished the open follow-up loop for this PR and there are no code changes pending on my side (last head unchanged in scope). This is currently blocked by workflow/action state () on maintainer side; could you rerun the required checks and/or review when convenient.

[Zakharden]

I’ve completed the PR updates from my side and there are no further code changes pending. This PR currently remains blocked by action/maintainer review state. Please rerun the necessary checks/review flow and I’ll respond immediately to anything still requested.