feat(github): Support Github multi org in Github installation pipeline

[Christinarlong]

Depends on #90342

This PR

1. Gets a user's installations from GitHub, filters through which one's the user is an owner of
2. Adds a new PipelineView
   • Returns a the UI page when the user has an existing installation they can choose
   • If there is no eligible existing installations, go to the next view (GithubInstallation)
3. In the GithubInstallation view, check if an existing installation was chosen if so, move to the next step (_finish_pipeline)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #90709       +/-   ##
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+ Coverage   53.25%   87.80%   +34.55%     
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  Files       10271    10279        +8     
  Lines      582624   583513      +889     
  Branches    22569    22566        -3     
===========================================
+ Hits       310291   512381   +202090     
+ Misses     271904    70703   -201201     
  Partials      429      429               

[cathteng]

could we make sure all changes are feature flagged? currently this will enable multi org as soon as it's merged.