chore(api-docs): Add documentation for GroupEventsEndpoint

[malwilley]

Ref https://github.com/getsentry/getsentry/issues/13865

Before:

After:

[github-actions[bot]]

🚨 Warning: This pull request contains Frontend and Backend changes!

It's discouraged to make changes to Sentry's Frontend and Backend in a single pull request. The Frontend and Backend are not atomically deployed. If the changes are interdependent of each other, they must be separated into two pull requests and be made forward or backwards compatible, such that the Backend or Frontend can be safely deployed independently.

Have questions? Please ask in the #discuss-dev-infra channel.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 87.50000% with 3 lines in your changes missing coverage. Please review.

:white_check_mark: All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/sentry/apidocs/hooks.py	0.00%	3 Missing :warning:

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #78575       +/-   ##
===========================================
+ Coverage   57.29%   78.23%   +20.94%     
===========================================
  Files        7094     7106       +12     
  Lines      312458   313015      +557     
  Branches    51024    51105       +81     
===========================================
+ Hits       179009   244893    +65884     
+ Misses     128766    61760    -67006     
- Partials     4683     6362     +1679