Fix bug with nuclio env variables

[arkravchuk]

Motivation and context

Fix bug with nuclio env variables.
os.getenv reads environment variables as strings. But the functions using PORT and DEFAULT_TIMEOUT expect it to be int

How has this been tested?

Checklist

• I submit my changes into the develop branch

• I have added a 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) 2022 Intel Corporation
#
# SPDX-License-Identifier: MIT

[nmanovic]

@arkravchuk , thanks for the contribution. Sorry that it took so much time to commit a couple of lines.