feat: add ai translations as a translation provider

[jansenk]

Added edx_ai_translations as a transcript provider option

I didn't want it to also be an option for TranscriptPreference.provider or ThirdPartyTranscriptCredentialsState.provier at this point .... potentially in the future?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.57%. Comparing base (189ec0a) to head (33a3c71).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #544      +/-   ##
==========================================
+ Coverage   94.56%   94.57%   +0.01%     
==========================================
  Files          31       32       +1     
  Lines        3165     3171       +6     
  Branches      122      122              
==========================================
+ Hits         2993     2999       +6     
  Misses        154      154              
  Partials       18       18              

Flag	Coverage Δ
unittests	94.57% <100.00%> (+0.01%)	⬆️

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[BrandonHBodine]

I don't think this will work without updating the line at

edx-val/edxval/api.py

Line 385 in 11521db

if provider and provider not in list(dict(TranscriptProviderType.CHOICES).keys()):

[BrandonHBodine]

Isn't the CHOICES enumeration already isolated to the VideoTranscript model?

[jansenk]

TranscriptPreference and ThirdPartyTranscriptCredentialsState also use this model