ci: add workflow to move inactive approvers/maintainers to emeritus

[pichlermarc]

Which problem is this PR solving?

This PR introduces partial automation for a task that is necessary but often emotionally taxing: maintaining accurate membership in the @open-telemetry/javascript-approvers and @open-telemetry/javascript-maintainers groups.

While the process of removing inactive members is not personal, it can feel personal. That emotional overhead tends to make this task harder than it should be, and often consumes more mental energy than the actual work involved. Automating parts of it helps reduce that burden and allows us to focus on finding new members to fill that role, rather than stressing over the removal part.

This initial automation focuses on Maintainers and Approvers as we:

• have the highest visibility and impact, requiring backfills when members step away.
• are expected to regularly review PRs, making activity assessment straightforward by checking for recent review activity.

The script uses very long threshold: 4 months of no review activity triggers a PR to propose moving a member to emeritus status. This PR still has to be manually approved by the remaining maintainers, and after the PR is merged, the group itself has to be manually updated. A single review within that period - regardless of whether it’s on their own PR or someone else's - prevents being auto-moved to emeritus. I chose this time frame to accommodate very-long vacations and other planned absences. For longer periods of inactivity, contributors are encouraged to reach out to the Maintainers.

I plan to further tweak the script in the coming months, including other members like Triagers and Component Owners as well.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.06%. Comparing base (52ffa04) to head (cc7f8c6).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5898   +/-   ##
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  Coverage   95.06%   95.06%           
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  Files         307      307           
  Lines        8031     8031           
  Branches     1627     1627           
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  Hits         7635     7635           
  Misses        396      396           

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