Add validation to CAM for Azure cluster-specific ResourceGroup configuration for snapshot copy

Originally filed by sseago: https://bugzilla.redhat.com/show_bug.cgi?id=1840315

Description of problem:
Migration using an Azure MigStorage with snapshot PV copy will fail if either src or dest cluster is missing the AzureResourceGroup spec field. We need a MigPlan validation which will prevent migration attempts for this case.

Version-Release number of selected component (if applicable):

How reproducible:
always

Steps to Reproduce:
1. Install CAM in an Azure host cluster, add an additional Azure MigCluster. One of these clusters should be configured without Spec.AzureResourceGroup being populated.
2. Create an Azure MigStorage.
3. Create a MigPlan to migrate a namespace which includes at least one Azure-backed PV between these two clusters, using the Azure MigStorage.
4. Configure the MigPlan to copy the PV by snapshot.
4. Start a migration.

Actual results:
Migration is attempted. The migration will fail if the src cluster is missing Spec.AzureResourceGroup. If the dest cluster is missing Spec.AzureResourceGroup, the migration may succeed but the PV will be created in the wrong ResourceGroup.

Expected results:
After configuring snapshot copy, the MigPlan should have a Fatal Condition added referencing the missing ResourceGroup param, preventing the user from being able to start a migration.