Reallocate TW headcount across sections/stages

Now that our Tech Writing team has grown, we need to begin reallocating section and stage coverage.

@mikelewis - Please make sure you’re not the assigned TW for any stage groups.

MR data to help (thanks, @marcel.amirault!): https://docs.google.com/spreadsheets/d/1KtqHMGOecGgnQTS_b5FmvlSZq7VWGOLu5jZDNcB53X4/edit#gid=0

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Updated stage/group assignments: https://docs.google.com/spreadsheets/d/1vrCG7N9d9XxKAR46xmu8axLaubZw9ESmzVkLyGotteQ/edit#gid=0

This is for "trainee" status as of 12.8 and assignment as of 12.9, per the onboarding process https://about.gitlab.com/handbook/engineering/technical-writing/#onboarding-technical-writers

Next:

• Add link to sheet from TW Handbook Assignments listing. gitlab-com/www-gitlab-com!38701 (merged)
• Add more detail to onboarding documentation about how to transition a stage/group. (Done, via templates.)
• Update Assignments listing at end of 12.8 milestone.
• Update Assignments listing at end of 12.9 milestone.
• Update Assignments listing at end of 12.10 milestone. (Latest changes are implemented per gitlab-com/www-gitlab-com!45856 (merged)).