[Layout] Add layout integration

[felixdittrich92]

This PR:

• Add layout predictor integration in ocr_predictor
• Update corresponding tests
• Update docs

TODO:

• Add model checkpoints
• Improve documentation (fine tune and include own layout model)
• Update README
• Update demo & API

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.92%. Comparing base (b45b899) to head (12a56bb).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2075      +/-   ##
==========================================
- Coverage   96.93%   96.92%   -0.02%     
==========================================
  Files         156      156              
  Lines        7415     7441      +26     
==========================================
+ Hits         7188     7212      +24     
- Misses        227      229       +2     

Flag	Coverage Δ
unittests	96.92% <100.00%> (-0.02%)	⬇️

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