Added ability to setup text labels content

[bsekachev]

Motivation and context

Sber request

How has this been tested?

Manual testing

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

[bsekachev]

Hi guys,

@TOsmanov Will you be able to add a piece of documentation?
@dvkruchinin Could you please add a test (or update case 111) to cover the feature?
@nstolyarov It was implemented to satisfy Sber request as we discussed on email. Can you take a look into how it works?

[dvkruchinin]

Could you please add a test (or update case 111) to cover the feature?

Hi. Sure. The test will be updated.

[bsekachev]

@ActiveChooN Could you please review?

[TOsmanov]

@TOsmanov Will you be able to add a piece of documentation?

@bsekachev Hi, sure.