Update Merge Request templates

What does this MR do?

• Adds Documentation MR template
• Refers to Distribution MR workflow in MR template
• Use first multiline commit in MR description (https://docs.gitlab.com/ee/user/project/description_templates.html#supported-variables-in-merge-request-templates)

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• (after merge) Remove the manually-entered default merge request description under Settings > Merge Requests > Default description template for merge requests

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Integration tests added to GitLab QA
• The impact any change in container size has should be evaluated