Fixing OCPBUGS-23793 in Update installation-creating-azure-service-principal.adoc

As per bug https://issues.redhat.com/browse/OCPBUGS-23793 changing the command for adding "user administrator access" to service principle.

Verified with my own test where the existing command from doc fails. 

$ az role assignment create --role "User Access Administrator" \
  --assignee-object-id $(az ad sp show --id <omitted> --query id -o tsv)

the following arguments are required: --scope

Author: Chin2691

modules/installation-creating-azure-service-principal.adoc

@@ -53,5 +53,7 @@ control. For more information, see https://aka.ms/azadsp-cli
 ----
 $ az role assignment create --role "User Access Administrator" \
   --assignee-object-id $(az ad sp show --id <appId> --query id -o tsv) <1>
+  --scope /subscriptions/<subscription_id> <2>
 ----
 <1> Specify the `appId` parameter value for your service principal.
+<2> Specifies the subscription ID.