Adding auxiliary experiment methods to Experiment class

[ItsMrLin]

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Summary: Adding auxiliary experiment methods to Experiment class to add (as first experiment) and find auxiliary experiment.

Meta: Add to first is needed as we currently support one aux PE experiment and the first one is the one with highest priority and is the one that will be used. Find aux experiment is needed to support pref opt config (see the diff on top), which will allow us to identify which PE exp to use instead of relying on the order.

Reviewed By: mgarrard

Differential Revision: D75696082

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D75696082

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 96.29630% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.88%. Comparing base (1336f0e) to head (f20cdc2). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
ax/core/experiment.py	91.66%	1 Missing :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3861   +/-   ##
=======================================
  Coverage   95.88%   95.88%           
=======================================
  Files         556      556           
  Lines       54786    54813   +27     
=======================================
+ Hits        52533    52559   +26     
- Misses       2253     2254    +1     

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[facebook-github-bot]

This pull request has been merged in facebook/Ax@82583c34c3024981f3d072a75ddf13cf7e6ce88d.