Fix model loading in datum explain

[vinnamkim]

Summary

• Resolve explain command cannot find the model  #721
• Fix model loading in datum explain
• Add an integration test for datum explain

How to test

This change will be covered in the added test.

Checklist

• I submit my changes into the develop branch
• I have added description of my changes into CHANGELOG
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues

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) 2021 Intel Corporation
#
# SPDX-License-Identifier: MIT

[codecov-commenter]

Codecov Report

Base: 83.93% // Head: 84.42% // Increases project coverage by +0.49% 🎉

Coverage data is based on head (b7d7c4f) compared to base (3aa4742).
Patch coverage: 33.33% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #804      +/-   ##
===========================================
+ Coverage    83.93%   84.42%   +0.49%     
===========================================
  Files          174      174              
  Lines        22941    22943       +2     
  Branches      4973     4974       +1     
===========================================
+ Hits         19255    19370     +115     
+ Misses        2559     2424     -135     
- Partials      1127     1149      +22     

Flag	Coverage Δ
macos-11_Python-3.10	83.94% <0.00%> (+0.10%)	⬆️
macos-11_Python-3.7	83.61% <0.00%> (+0.07%)	⬆️
macos-11_Python-3.8	83.87% <0.00%> (+0.09%)	⬆️
macos-11_Python-3.9	83.88% <0.00%> (+0.09%)	⬆️
ubuntu-20.04_Python-3.10	84.34% <33.33%> (+0.48%)	⬆️
ubuntu-20.04_Python-3.7	84.02% <33.33%> (+0.47%)	⬆️
ubuntu-20.04_Python-3.8	84.28% <33.33%> (+0.48%)	⬆️
ubuntu-20.04_Python-3.9	84.29% <33.33%> (+0.48%)	⬆️
windows-2019_Python-3.10	84.30% <33.33%> (+0.49%)	⬆️
windows-2019_Python-3.7	83.97% <33.33%> (+0.47%)	⬆️
windows-2019_Python-3.8	84.22% <33.33%> (+0.49%)	⬆️
windows-2019_Python-3.9	84.24% <33.33%> (+0.49%)	⬆️

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

Impacted Files	Coverage Δ
datumaro/cli/commands/explain.py	55.43% <33.33%> (+19.87%)	⬆️
datumaro/components/project.py	80.84% <0.00%> (+0.06%)	⬆️
datumaro/plugins/splitter.py	88.69% <0.00%> (+0.22%)	⬆️
datumaro/util/annotation_util.py	74.19% <0.00%> (+0.64%)	⬆️
datumaro/components/algorithms/rise.py	89.65% <0.00%> (+0.68%)	⬆️
datumaro/util/image.py	91.57% <0.00%> (+1.12%)	⬆️
datumaro/util/telemetry_utils.py	79.16% <0.00%> (+3.33%)	⬆️
datumaro/cli/contexts/model.py	65.41% <0.00%> (+12.78%)	⬆️
datumaro/plugins/openvino_plugin/launcher.py	60.48% <0.00%> (+55.64%)	⬆️

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[bonhunko]

looks good! I left a comment only for a typo thing.

[sooahleex]

Looks good to me.