{AKS} Update the implementation of aks create to adopt the decorator pattern

[FumingZhang]

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

Update the implementation of aks create to adopt the decorator pattern.

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]

AKS

[wangzelin007]

LGTM

[FumingZhang]

Backward compatibility test results pipeline 1 & pipeline 2.

[FumingZhang]

New backward compatibility test:

• All test cases included by default: result 1
• Rerun the previously failed test case (attach acr): result 2

aks-preview extended test:

• All test cases excluded by default: result 1
• Rerun the previously failed test cases: result 2
• Rerun the previously failed test case (pod identity): result 3
• Invalid test case: test_aks_create_with_http_proxy_config