[ARM] az deployment sub/group what-if：Add new commands to support What-If for ARM template deployment

[shenglol]

Description of PR (Mandatory)
The PR adds new commands for ARM template deployment What-If (in preview):

• az deployment sub what-if
• az deployment group what-if

which can tell users what will happen when they deploy a template if it is valid.

A new flag --confirm-with-what-if was also added to the existing deployment sub/group create commands to allow users to review and acknowledge resource changes and execute deployment with one operation.

Here's a sample output:

Testing Guide
(Example commands with explanations)

History Notes:
(Fill in the following template if multiple notes are needed, otherwise PR title will be used for history note.)

[ARM] Add template deployment What-If commands

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[yonzhan]

add to S168

[zhoxing-ms]

@shenglol Why doesn't az deployment mg, az deployment tenant have what-if?

[zhoxing-ms]

I suggest that it might be better to change the PR title, like: [ARM] az deployment sub/group/... what-if：Add new commands to support What-If for ARM template deployment
PR title writing guide: link

[shenglol]

@shenglol Why doesn't az deployment mg, az deployment tenant have what-if?

Currently the What-If back-end doesn't support mg-level and tenant-level deployments. We might add the support in the future.

[shenglol]

I suggest that it might be better to change the PR title, like: [ARM] az deployment sub/group/... what-if：Add new commands to support What-If for ARM template deployment
PR title writing guide: link

Thanks. I changed the title.

[shenglol]

@zhoxing-ms @jiasli do you mind helping merge it once the build pipeline passes? It would be great if we can still catch the next release.

[jiasli]

@zhoxing-ms @jiasli do you mind helping merge it once the build pipe line passes? It would be great if we can still catch the next release.

Absolutely!

[shenglol]

@Juliehzl could you take another look at the PR when you get a chance? Thanks!

[Juliehzl]

@Juliehzl could you take another look at the PR when you get a chance? Thanks!

LGTM in general but curious about the fantastic function you add. 😊

[Juliehzl]

We also need to use get_model() here.

Can you use mock() to test as shown here https://github.com/Azure/azure-cli/blob/dev/src/azure-cli/azure/cli/command_modules/appservice/tests/latest/test_webapp_commands_thru_mock.py#L85?

[shenglol]

Replaced import with get_model(). Regarding using mock(), I don't think it's needed in the formatters unit tests (since there's no dependencies to assert/verify), but I added two tests with mocks to verify prompt logic with -confirm-with-what-if, which seems to be worth testing to me: https://github.com/Azure/azure-cli/pull/12942/files#diff-a94496ee0aa9c24d38ce3e3e2793c8a2R337-R358.