Remove deprecated community advocacy handbook & update community relations workflows

Why is this change being made?

The community advocacy program was discontinued in 2020. The deprecated handbook causes confusion on currently supported workflows. This MR removes the /community-advocacy/ directory and updates all surrounding workflows.

If we need to restore or move a workflow, we can checkout an older Git commit and copy the content, if applicable.

Closes https://gitlab.com/gitlab-com/marketing/community-relations/community-operations/community-operations/-/issues/133

Changes

• Remove /community-advocacy/ handbook
• Update marketing/corporate marketing references
• Update engineering/product/content references
• Add Community Relations emergency contacts, including a new doc https://docs.google.com/document/d/16oq7sl6dpI2QbADwY41KjKEjaEj7dJ9LI5owm8lO_iU/edit
• Create new redirects where applicable

Not changed

• all-remote https://about.gitlab.com/company/culture/all-remote/people/#community-advocates is a different term for community advocates
• Keep the job family - this needs to be removed separately, linked into the compensation calculator, and people group processes
• data/projects.yaml lists https://gitlab.com/gitlab-com/marketing/community-relations/community-advocacy/tanukidesk which needs to be deprecated separately.

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
  • Copy/paste the Slack conversation to document it for later, or upload screenshots. Verify that no confidential data is added.
• Assign reviewers for this change to the correct DRI(s)
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the "Maintained by" section in on the page being edited.
  • 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 affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR.
  • If this is a change that directly impacts the majority of global team members, it should be a candidate for #company-fyi. Please work with internal communications and check the handbook for examples.

---