Add check for vnet location for Azure Spring Cloud

[gavinfish]

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For VNet Injection instance, Azure Spring Cloud instance should be in the same location as the target VNet.

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/$EXT "git+https://github.com/VSChina/azure-cli-extensions.git@jieshe/vnet-location#subdirectory=src/$EXT&egg=$EXT"

[yungezz]

will there be format difference? like west us vs westus. :)

[gavinfish]

Fixed.

[yungezz]

pls resolve conflict, then good to go.