Update handbook TW Lead items. Include discussion on Removals, Upgrades for all

Why is this change being made?

Clarify the handbook list of duties. Goal: better guidance to the TW Lead for each release.

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to your manager.
  • 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.
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files.

For help with failing pipelines reach out in #mr-buddies in Slack

Open issue with this MR -- we don't have a true SSoT for our RP checklists; is it this handbook page or is it the applicable MR checklist? But in the interests of MVC, I've aligned them as closely as I can.

This is a relatively long MR; I've interspersed comments to describe what I've done in different sections.

You can review the build here: https://mjang-13-0-tw-lead-updates.about.gitlab-review.app/handbook/marketing/blog/release-posts/index.html