Allow admins to access registrar console without a RegistrarContact

This allows admins to access the registrar console without needing to be added
as a registrar contact. If they are a registrar contact, then that registrar
takes precedence.

Tested=In Alpha

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=164182623

java/google/registry/config/files/default-config.yaml

@@ -71,6 +71,11 @@ registryPolicy:
   # domain checks.
   checkApiServletClientId: TheRegistrar
 
+  # The registry admin's registrar. Admins are granted permission to log in
+  # using this registrar automatically if they are not associated with any
+  # registrar
+  registryAdminClientId: TheRegistrar
+
   # Disclaimer at the top of the exported reserved terms list.
   reservedTermsExportDisclaimer: |
     This list contains reserved terms for the TLD. Other terms may be reserved

java/google/registry/config/files/nomulus-config-production-sample.yaml

@@ -29,6 +29,7 @@ registryPolicy:
   tmchCrlUrl: http://crl.icann.org/tmch.crl
   tmchMarksDbUrl: https://ry.marksdb.org
   checkApiServletClientId: placeholder
+  registryAdminClientId: placeholder
   whoisDisclaimer: |
     multi-line
     placeholder