New extension Swiftlet

[qwordy]

Resolve Azure/azure-cli#14418

---

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.

[azuresdkci]

If this PR is for a new extension or change to an existing extension, use the following to try out the changes in this PR:

docker run -it microsoft/azure-cli:latest
export EXT=<NAME>
pip install --upgrade --target ~/.azure/cliextensions/$EXT "git+https://github.com/qwordy/azure-cli-extensions.git@swiftlet#subdirectory=src/$EXT&egg=$EXT"

[yungezz]

hi @fengzhou-msft could you pls help to review?thanks

[qwordy]

Do not review generated code if I rewrite them in manual folder.

[fengzhou-msft]

Add a . in the end.