"management delete" should show workload clusters before proceeding

[mboersma]

#139 changed the behavior of az capi management delete actually to delete the management cluster after confirmation, as we agreed this is the expected behavior. This new behavior could be further improved by showing any existing workload clusters before asking for confirmation:

Please note that "my-cluster" is managing workload clusters:
NAMESPACE   NAME            PHASE         AGE     VERSION
default     default-20520   Provisioned   22m11s
default     default-32106   Provisioned   2m28s
default     default-70206   Provisioning  45s

Deleting the management cluster will leave these workload clusters in their
current configuration, without a way to manage them.

But this would probably have to be implemented as a "best effort" strategy, since it's possible the management cluster has failed or become inaccessible (hence the user is deleting it).

See https://github.com/Azure/azure-capi-cli-extension/pull/139/files#r891383438 for more context.

[bennycortese]

/assign

[mboersma]

@bennycortese do you still intend to work on this? Otherwise, I'll unassign it so it's available for contributors.

[bennycortese]

You can unassign it from me, sorry life got kind of busy lately