add boxes-to-polygons transform

[jihyeonyi]

Summary

Add bbox to polygon transform.

How to test

Checklist

• I have added unit tests to cover my changes.​
• I have added integration tests to cover my changes.​
• I have added the description of my changes into CHANGELOG.​
• I have updated the documentation accordingly

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.
• I have updated the license header for each file (see an example below).

# Copyright (C) 2023 Intel Corporation
#
# SPDX-License-Identifier: MIT

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (c84a13d) 80.00% compared to head (7f1b93c) 80.01%.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1119   +/-   ##
========================================
  Coverage    80.00%   80.01%           
========================================
  Files          258      258           
  Lines        29329    29336    +7     
  Branches      5745     5746    +1     
========================================
+ Hits         23465    23473    +8     
  Misses        4516     4516           
+ Partials      1348     1347    -1     

Flag	Coverage Δ
macos-11_Python-3.8	79.10% <100.00%> (+<0.01%)	⬆️
ubuntu-20.04_Python-3.8	79.99% <100.00%> (+<0.01%)	⬆️
windows-2019_Python-3.8	79.92% <100.00%> (+<0.01%)	⬆️

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

Files Changed	Coverage Δ
src/datumaro/plugins/transforms.py	76.52% <100.00%> (+0.23%)	⬆️

... and 1 file with indirect coverage changes

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[vinnamkim]

LGTM.