Use overall_from_subgrades field for the total robogrades values

[sarikaya]

Motivation and context

How has this been tested?

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

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  Feel free to contact the maintainers if that's a concern.
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# Copyright (C) 2021 Intel Corporation
#
# SPDX-License-Identifier: MIT