Refactor download CLI command

[vinnamkim]

Summary

• Move "datum describe-downloads" -> "datum download describe"
• Move "datum download" -> "datum download get"
• Refactor datum download cli test to use pytest framework
• Ticket no. 107277

How to test

I refactor the CLI test for this change as well.

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: 18.64% and project coverage change: -0.03 ⚠️

Comparison is base (8270e64) 78.90% compared to head (4f07d02) 78.88%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #909      +/-   ##
===========================================
- Coverage    78.90%   78.88%   -0.03%     
===========================================
  Files          211      210       -1     
  Lines        25059    25065       +6     
  Branches      5031     5032       +1     
===========================================
- Hits         19774    19773       -1     
- Misses        4152     4159       +7     
  Partials      1133     1133              

Flag	Coverage Δ
macos-11_Python-3.8	77.87% <18.64%> (-0.03%)	⬇️
ubuntu-20.04_Python-3.8	78.87% <18.64%> (-0.03%)	⬇️
windows-2019_Python-3.8	78.82% <18.64%> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
datumaro/cli/__main__.py	0.00% <ø> (ø)
datumaro/cli/commands/no_project/download.py	17.85% <17.85%> (ø)
datumaro/cli/util/__init__.py	28.30% <20.00%> (-0.87%)	⬇️
datumaro/cli/commands/__init__.py	100.00% <100.00%> (ø)

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[wonjuleee]

Overall it looks good to me. But I am not sure whether no_project is appropriate or not. It could be related to which commands are more general and preferable to users between w/ project or wo/ project. If wo/ project is more general, it would be good to move them in an independent directory. What do you think?

[vinnamkim]

Overall it looks good to me. But I am not sure whether no_project is appropriate or not. It could be related to which commands are more general and preferable to users between w/ project or wo/ project. If wo/ project is more general, it would be good to move them in an independent directory. What do you think?

It will be re-refactored in #910 again. We can continue this discussion in that PR.