Include the performing user in the "Registrar updated" emails

Whenever a registrar is changed via the registrar console, we send out a
notification of that change.

Since we're going to allow Admins and soon Vendors to use the console in
addition to the registrars, it becomes important to know who actually performed
the changes if the registrars complain.

In addition, we will now send notifications for changes in Sandbox since we're
going to actually allow registrars to update sandbox data.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=217539534

java/google/registry/request/auth/AuthResult.java

@@ -38,7 +38,11 @@ public abstract class AuthResult {
 
   public String userIdForLogging() {
     return userAuthInfo()
-        .map(userAuthInfo -> userAuthInfo.user().getEmail())
+        .map(
+            userAuthInfo ->
+                String.format(
+                    "%s %s",
+                    userAuthInfo.isUserAdmin() ? "admin" : "user", userAuthInfo.user().getEmail()))
         .orElse("<logged-out user>");
   }