Added throttling policy for unauthenticated users

[azhavoro]

Added throttling policy for unauthenticated users.

Motivation and context

It's a good practice to have throttling policy for REST API to reduce security risks.

How has this been tested?

Manually

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)

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) 2020 Intel Corporation
#
# SPDX-License-Identifier: MIT

[nmanovic]

@azhavoro , any problems with the patch?

[coveralls]

Pull Request Test Coverage Report for Build 5367

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.009%) to 65.657%

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Files with Coverage Reduction	New Missed Lines	%
datumaro/datumaro/components/project.py	1	77.49%

Totals
Change from base Build 5360:	-0.009%
Covered Lines:	10837
Relevant Lines:	16101

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💛 - Coveralls

[nmanovic]

LGTM