Add allocationBlockPrefixSize to support vnetBlock

[isaac-dasan]

Related command

az dnc create

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]

⚠️Azure CLI Extensions Breaking Change Test

⚠️dnc

rule	cmd_name	rule_message	suggest_message
⚠️ 1006 - ParaAdd	dnc delegated-subnet-service create	cmd dnc delegated-subnet-service create added parameter allocation_block_prefix_size

[yonzhan]

Thank you for your contribution! We will review the pull request and get back to you soon.

[azclibot]

[Release] Update index.json for extension [ dnc ] : https://dev.azure.com/azclitools/internal/_build/results?buildId=85057&view=results