[AD] az ad app/sp update: Support generic update --set on root level

[jiasli]

Related command
az ad app update
az ad sp update

Description
Close #22758, #22777, #22635

az ad sp update has no native arguments, but only generic update arguments:

> az ad sp update -h

Command
    az ad sp update : Update a service principal.

Arguments
    --id    [Required] : Service principal name, or object id.

Generic Update Arguments
    --add              : Add an object to a list of objects by specifying a path and key value
                         pairs.  Example: --add property.listProperty <key=value, string or JSON
                         string>.
    --force-string     : When using 'set' or 'add', preserve string literals instead of attempting
                         to convert to JSON.
    --remove           : Remove a property or an element from a list.  Example: --remove
                         property.list <indexToRemove> OR --remove propertyToRemove.
    --set              : Update an object by specifying a property path and value to set.  Example:
                         --set property1.property2=<value>.

https://docs.microsoft.com/en-us/cli/azure/microsoft-graph-migration#known-issues documented that generic update arguments are not supported by now. Therefore, az ad sp update is basically a no-op.

This PR is an initial attempt to makes generic update work with the new model-less framework by supporting generic update --set for az ad app/sp update on the root level:

ad app update --id {app_id} --set isDeviceOnlyAuthSupported=true
az ad sp update --id 233dd73b-72e3-424a-9367-7588d957267e --set 'tags=["mytag"]'

[jiasli]

AD Graph SDK uses verb "patch", instead of "update": azure.graphrbac.operations.applications_operations.ApplicationsOperations.patch. I guess it is used to differentiate with update_application of generic update.

We switch to use "update" to align with other update operations (such as azure.graphrbac.operations.users_operations.UsersOperations.update) and the API document https://docs.microsoft.com/en-us/graph/api/application-update.

[jiasli]

The underlying functionality support of --set is

azure-cli/src/azure-cli-core/azure/cli/core/commands/arm.py

Lines 502 to 503 in ce3a1f1

	elif isinstance(instance, dict):
	instance[name] = value