[misc] increase to 0.8.0 and temp pin onnx

[felixT2K]

This PR:

• increase version to 0.8.0 (docker feature / orientation improvement / etc. -> minor instead of patch)
• temp pin onnx until [DO NOT MERGE]Check onnx 1.15 rc 1. onnx/tensorflow-onnx#2252 is fixed

[codecov]

Codecov Report

Merging #1365 (9834827) into main (bc2d3c5) will decrease coverage by 0.01%.
Report is 5 commits behind head on main.
The diff coverage is 97.67%.

@@            Coverage Diff             @@
##             main    #1365      +/-   ##
==========================================
- Coverage   95.80%   95.79%   -0.01%     
==========================================
  Files         154      155       +1     
  Lines        6909     6952      +43     
==========================================
+ Hits         6619     6660      +41     
- Misses        290      292       +2     

Flag	Coverage Δ
unittests	95.79% <97.67%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
doctr/datasets/__init__.py	100.00% <100.00%> (ø)
doctr/models/recognition/sar/pytorch.py	97.29% <ø> (ø)
doctr/models/recognition/vitstr/pytorch.py	100.00% <ø> (ø)
doctr/datasets/wildreceipt.py	97.61% <97.61%> (ø)

... and 1 file with indirect coverage changes

[felixdittrich92]

@odulcy-mindee forced to fix CI