docs(MAINTAINING): update release section + add team section

[jsjoeio]

This PR updates the MAINTAINING docs, specifically:

• adds Team section with Onboarding and Offboardng sections
• adds notes around release platforms
• updates release instructions with step for naming version branch correctly

Fixes #3894
Fixes #4174

[codecov]

Codecov Report

Merging #4234 (6b079e6) into main (f3ef414) will not change coverage.
The diff coverage is n/a.

❗ Current head 6b079e6 differs from pull request most recent head c91033c. Consider uploading reports for the commit c91033c to get more accurate results

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  Coverage   65.09%   65.09%           
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  Files          36       36           
  Lines        1882     1882           
  Branches      380      380           
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  Hits         1225     1225           
  Misses        559      559           
  Partials       98       98           

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[github-actions]

✨ Coder.com for PR #4234 deployed! It will be updated on every commit.

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[bryphe-coder]

Looks good! Nice job documenting the process @jsjoeio