Add Azure Identity Authority Selector (#176)

* New AzureSettings to select the Identity Authority

* Add fallback for existing customers

* Throw error if Identity Authority is set to invalid value

src/locales/en/messages.json

@@ -354,6 +354,9 @@
     "rootPath": {
         "message": "Root Path"
     },
+    "identityAuthority": {
+        "message": "Identity Authority"
+    },
     "tenant": {
         "message": "Tenant"
     },