Enable granularity for which controllers to run

[enxebre]

/kind feature

Describe the solution you'd like
As a cluster service provider managing a multi-tenant environment I would like to setup my capi controllers to watch only well known targeted resources and do not run unnecessary controllers. E.g If I'm targeting aro/aks clusters I don't need to run the AzureMachine or the AzureCluster controllers or if I'm using AzureMachine with externally managed infra I don't need ASOAPI

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

• cluster-api-provider-azure version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

[damdo]

/cc @nojnhuh @mboersma @jackfrancis

[bryan-cox]

This helps some with this - #5099

[patrickdillon]

This would also be helpful to disable the AzureJSONMachineController. We do not use CAPZ to manage the cloud provider (config or authentication), but that controller emits a concerning warning (which is not accurate in our case):

cluster-api-provider-azure/controllers/helpers.go

Lines 67 to 69 in a6c301f

	spIdentityWarning = "You are using Service Principal authentication for Cloud Provider Azure which is less secure than Managed Identity. " +
	"Your Service Principal credentials will be written to a file on the disk of each VM in order to be accessible by Cloud Provider. " +
	"To learn more, see https://capz.sigs.k8s.io/topics/identities-use-cases.html#azure-host-identity "