Add ImageColorScale context manager

[vinnamkim]

Summary

• To utilize Datumaro as the data pipeline frontend for model training, it is crucial to ensure that the input image's color format consistently adheres to the 3-channel requirement. This is a common practice for many model training frameworks. This pull request introduces a context manager designed to enforce the acquisition of raw images in Datumaro (e.g., data.media_as(Image).data) in the 3-channel.

How to test

I added some tests for this change.

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]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (b163010) 80.06% compared to head (26b0f99) 80.07%.

Files	Patch %	Lines
src/datumaro/util/image.py	92.10%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1194   +/-   ##
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  Coverage    80.06%   80.07%           
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  Files          268      268           
  Lines        29849    29862   +13     
  Branches      5847     5846    -1     
========================================
+ Hits         23898    23911   +13     
+ Misses        4618     4617    -1     
- Partials      1333     1334    +1     

Flag	Coverage Δ
macos-11_Python-3.8	79.19% <92.10%> (+<0.01%)	⬆️
ubuntu-20.04_Python-3.8	80.06% <92.10%> (+<0.01%)	⬆️
windows-2022_Python-3.8	80.03% <92.10%> (+<0.01%)	⬆️

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[wonjuleee]

LGTM!