Organise OpenAPI schema for transcriptions and classifications

In the API schema, classifications and transcriptions endpoints are mixed together in the ml category, which is confusing.
It would be cleaner to separate them into two categories transcriptions and classifications. Part of #261 (closed)

changed the description

added 4 commits

• a1ebd8f9...797339dc - 2 commits from branch master
• 9b1ef503 - Move transcriptions
• b67e7a39 - Move classifications

Compare with previous version

Codecov Report

Merging #790 into master will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #790   +/-   ##
=======================================
  Coverage   86.44%   86.44%           
=======================================
  Files         205      205           
  Lines       13644    13645    +1     
=======================================
+ Hits        11795    11796    +1     
  Misses       1849     1849           

Impacted Files	Coverage Δ
arkindex/documents/api/elements.py	98.70% <ø> (ø)
arkindex/documents/api/ml.py	96.89% <100.00%> (+0.01%)

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mentioned in commit de9da9e9

merged