add remaining n input constructor

[mgarrard]

Summary: This diff adds the input constructor for our default logic for repeat arms. See note in comments about how this new logic differs Follow up diffs:

• update the transition logic to leverage this
• storage --> let's do this once we all like the 3 input constructors
• update the input constructors to handle the case where n isn't provided as a kwarg
• add tests for real world scenario per Liz suggestion
• add test to enforce signature across input constructors per Liz/Sait/Daniel suggestion

Differential Revision: D62467907

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This pull request was exported from Phabricator. Differential Revision: D62467907

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This pull request was exported from Phabricator. Differential Revision: D62467907

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.68%. Comparing base (2e7291e) to head (d986cad). Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
.../modelbridge/generation_node_input_constructors.py	96.96%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2758 +/- ## ======================================= Coverage 95.67% 95.68% ======================================= Files 486 488 +2 Lines 47713 47802 +89 ======================================= + Hits 45650 45738 +88 - Misses 2063 2064 +1 ```

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This pull request was exported from Phabricator. Differential Revision: D62467907

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This pull request was exported from Phabricator. Differential Revision: D62467907

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This pull request has been merged in facebook/Ax@a880c3a53570de1fd30231ce0f6796c4c02b7352.