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/RegistryConfigSettings.java

@@ -78,6 +78,7 @@ public class RegistryConfigSettings {
     public String tmchCrlUrl;
     public String tmchMarksDbUrl;
     public String checkApiServletClientId;
+    public String registryAdminClientId;
     public String reservedTermsExportDisclaimer;
     public String whoisDisclaimer;
   }