docs: Add merge request acceptance checklist

What does this MR do and why?

This merge request aims to improve efficiency for maintainers and contributors by adding checklists for the MR acceptance/merge workflows and clarifying caveats around non-conventional commits.

1. Create a new merge request template with checklists for contributors and maintainers.
2. Add a note on fixup! commits marking MRs as Draft.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

1. Read the new template and documentation changes rendered as markdown in this MR. 😉

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

Contributors

• I have evaluated the MR acceptance checklist for this MR.

• I have added requested a review from a maintainer:

  Hey @pslaughter! Can you please review and merge this MR? Thanks!
  
  /assign_reviewer @pslaughter

Maintainers

• Review the functionality.
• Review the maintainability.
• Approve the MR.
• Add the MR to the merge train