external directory: reset auth source when disabled

this allows existing users to login (including the owner itself)

The alternative is to have some system where we have unique superadmin users across cloudrons which don’t get trampled upon by a sync. This is a bit unrealistic. For the future, we could also design this such that ldap auth is asked for in the initial step i.e at superadmin creation time.

If LDAP connection is lost/down, user can always use 'cloudron-support —owner-login'

dashboard/src/translation/en.json

@@ -244,7 +244,8 @@
             "bindPassword": "Bind Password (optional)",
             "errorSelfSignedCert": "Server is using an invalid or self-signed certificate.",
             "providerOther": "Other",
-            "providerDisabled": "Disabled"
+            "providerDisabled": "Disabled",
+            "disableWarning": "The authentication source of all existing users will be reset to authenticate against the local password database."
         },
         "subscriptionDialog": {
             "title": "Subscription required",