[Datumaro] Add model info and source info commands

[zhiltsov-max]

Motivation and context

• Added model info and source info commands to print corresponding configurations

How has this been tested?

Manual test

Checklist

• I submit my changes into the develop branch
• I have added description of my changes into CHANGELOG file
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (read github docs)
• I have increased versions of npm packages if it is necessary (cvat-canvas,
  cvat-core, cvat-data and cvat-ui)

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) 2020 Intel Corporation
#
# SPDX-License-Identifier: MIT

[coveralls]

Pull Request Test Coverage Report for Build 6765

• 4 of 38 (10.53%) changed or added relevant lines in 3 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 68.963%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
datumaro/datumaro/cli/contexts/project/init.py	0	4	0.0%
datumaro/datumaro/cli/contexts/model/init.py	2	17	11.76%
datumaro/datumaro/cli/contexts/source/init.py	2	17	11.76%

Files with Coverage Reduction	New Missed Lines	%
datumaro/datumaro/cli/contexts/project/init.py	2	9.69%

Totals
Change from base Build 6761:	-0.1%
Covered Lines:	11149
Relevant Lines:	15655

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💛 - Coveralls