Webpack dev server proxy

[ActiveChooN]

Motivation and context

Added proxy to webpack dev server config to exclude server API variable from UI code and make cypress tests executable on the local environment.

How has this been tested?

No tests

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]

Can't open admin page when built locally:

Probably need to update defaults in cvat-core/src/config.js also

[bsekachev]

Also when I open a task page:

Also I would recommend to check Analytics button.