Allow full configuration of nuclio

[subdavis]

Motivation and context

It is not currently possible to deploy nuclio properly into a cloud environment and connect it with a CVAT installation. Port and scheme are hard-coded even though Nuclio might be running behind a load balancer with HTTPS enabled.

How has this been tested?

Tested in docker compose using my own compose override file that adds these new environment variables.

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 Not applicable, no documentation for the existing feature exists, so nowhere to add.
• I have added tests to cover my changes Not applicable, no tests exist
• I have linked related issues (read github docs) Not applicable
• I have increased versions of npm packages if it is necessary (cvat-canvas,
  cvat-core, cvat-data and cvat-ui) Not applicable

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) Not applicable

# Copyright (C) 2021 Intel Corporation
#
# SPDX-License-Identifier: MIT

[nmanovic]

@subdavis , thanks for the contribution. It looks fine. In general you always can redefine settings for your local CVAT instance (from cvat.settings.production import * and modify that you like, after that use DJANGO_SETTINGS_MODULE). But let's keep env variables to simplify things.