ci: add comment on PRs targeting main

[Buckwich]

Related to bpmn-io/internal-docs#1206

Proposed Changes

Add a github action that adds a comment if the target branch of a PR is main, (we want to target develop by default).

See for example the comment in this PR. But in this case I actually want to target main directly

I also noticed a workflow name not matching its content. renamed the file

Checklist

To ensure you provided everything we need to look at your PR:

• Brief textual description of the changes present
• Visual demo attached
• Steps to try out present, i.e. using the @bpmn-io/sr tool
• Related issue linked via Closes {LINK_TO_ISSUE} or Related to {LINK_TO_ISSUE}

[github-actions]

This pull request targets the main branch. Please target main for bug fixes only. Target develop for regular feature development.