HDDS-15566. Move feature branch merge checklist to the website

[errose28]

What changes were proposed in this pull request?

Move the feature branch merge checklist from confluence to the new website. As part of this change:

• The checklist was updated
• Docs on the project's git usage were rearranged to make room for the new content
• All existing branch merge checklists from confluence were reformatted to markdown by AI and imported here
• A process to raise new branch merge checklists as PRs to this repo for review is proposed

What is the link to the Apache Jira?

HDDS-15566

How was this patch tested?

Local preview

[errose28]

@gardenia This is the switch of the branch merge checklist to the new website I mentioned at the community sync.

[errose28]

@jojochuang @adoroszlai can you read through this branch merge checklist proposal and provide some initial feedback? I'd like to share this on the dev list for broader consensus on 02-merge-checklist.md once we have some initial agreement.