[CosmosDB]: az cosmosdb dts: Add cosmos db data transfer commands

[niteshvijay1995]

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This checklist is used to make sure that common guidelines for a pull request are followed.

General Guidelines

• Have you run azdev style <YOUR_EXT> locally? (pip install azdev required)
• Have you run python scripts/ci/test_index.py -q locally?

For new extensions:

• My extension description/summary conforms to the Extension Summary Guidelines.

About Extension Publish

There is a pipeline to automatically build, upload and publish extension wheels.
Once your PR is merged into master branch, a new PR will be created to update src/index.json automatically.
The precondition is to put your code inside this repo and upgrade the version in the PR but do not modify src/index.json.

[yonzhan]

cosmosdb

[calvinhzy]

Please add some tests if possible.

[evelyn-ys]

1. Please add tests for newly added commands.
2. Don't forget to update version in setup.py and History.rst

[niteshvijay1995]

Added tests

[evelyn-ys]

LGTM in general