Update maintainer MR templates around giving feedback

Why is this change being made?

This merge request updates the content of the merge request templates used when we want someone to become a maintainer. In a recent process update we changed the way of providing feedback, but this has not been updated in the templates.

@oregand @m_gill can you please review this merge request and check if the content here is accurate and in-line with our Handbook page. I see that these templates are not mentioned on that page, is that expected?

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this MR to the correct Directly Responsible Individual/s (DRI)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the Maintained by section on the page being edited
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies

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