Add ModelBridgeNotImplementedError

[saitcakmak]

Summary: ModelBridge._fit_if_implemented catches NotImplementedError to support subclasses that do not need to fit any models. However, NotImplementedError is too generic of an error type to catch and may mask other issues lower in the stack. Defining a specific class for the intentionally not implemented methods will allow us to catch only what we intend to and raise the unexpected errors.

Differential Revision: D65948196

[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D65948196

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 75.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 95.69%. Comparing base (9142af8) to head (1f3e21f). Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
ax/modelbridge/base.py	66.66%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3068 +/- ## ======================================= Coverage 95.69% 95.69% ======================================= Files 487 487 Lines 49342 49344 +2 ======================================= + Hits 47217 47219 +2 Misses 2125 2125 ```

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[facebook-github-bot]

This pull request was exported from Phabricator. Differential Revision: D65948196

[facebook-github-bot]

This pull request has been merged in facebook/Ax@49698fceeb1c7f65f8ba598253c6de94875c1163.