[IoT] Adds IoT Extension Release v0.21.1

[c-ryan-k]

Notes for this release can be found here:
https://github.com/Azure/azure-iot-cli-extension/releases/tag/v0.21.1

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

Related command

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 pull request is merged into main branch, a new pull request will be created to update src/index.json automatically.
You only need to update the version information in file setup.py and historical information in file HISTORY.rst in your PR but do not modify src/index.json.

[azure-client-tools-bot-prd]

Hi @c-ryan-k,
Since the current milestone time is less than 7 days, this pr will be reviewed in the next milestone.

[yonzhan]

IoT