Re-write release test plan document to account for newly automated parts

[dbjorge]

• Remove steps already covered by automation
• Ensure manual steps still exist for any cases we couldn't automate
• Ensure manual steps still exist for appropriate cases considered during Audit recent validation notes for bugs caught #904

As part of this, consider whether to keep using our internal onenote for this, vs using a more public process like VSCode's "endgame-plan" issues (example)

[dbjorge]

Rewrote onenote page accordingly. Did not have time to consider endgame-plan approach.