Replace Nginx proxy with Traefik

[tadejsv]

Motivation and context

This replaces the Nginx with a more "modern" proxy, Traefik.
There should be no change in the basic usage, i.e. the new docker-compose.yml file is a drop-in replacement for the old one. For using HTTPS the process becomes vastly simplified, and boils down to setting 2 env variables and using an override docker compose file.

Apart from HTTPS, the only other noticeable user-facing change is that the hostname is no longer set by the CVAT_HOST env variable in the proxy service, but by the CVAT_HOST env variable in the shell from which the user will execute the docker-compose command.

Closes #3407.

How has this been tested?

I have tested the new docker-compose.yml file locally, and I have also tested the docker-compose.https.yml file on an EC2 instance with my own domain - HTTPS was properly set up, as expected. But it would be great if someone else would test this on their own, just to double-check.

Also, I am not sure how this would work with proxy (in this sense). Should anyone be able to help me with checking this, that would be great.

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

[tadejsv]

@nmanovic This PR is now ready for review

[tadejsv]

@nmanovic Would you mind running the workflows here again?

[azhavoro]

@tadejsv Hi,

Thanks for the contribution, great job!
I have 2 comments:

• Could you please update the network section of https://github.com/openvinotoolkit/cvat/blob/develop/components/analytics/docker-compose.analytics.yml as well
• Please fix conflicts and linter issues for changelog.md

[tadejsv]

Thanks for the feedback, @azhavoro . I have implemented the changes you suggested. If you re-run the workflows, I think all tests should pass

[nmanovic]

@tadejsv , great job! Thanks for the contribution.