Initial, easy changes to support later addition of RDAP metrics

I split this out to avoid having a giant CL that changes everything. The actual
metrics will follow later.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=174356874

java/google/registry/rdap/RdapNameserverAction.java

@@ -24,6 +24,7 @@ import com.google.common.collect.ImmutableMap;
 import google.registry.flows.EppException;
 import google.registry.model.host.HostResource;
 import google.registry.rdap.RdapJsonFormatter.OutputDataType;
+import google.registry.rdap.RdapMetrics.EndpointType;
 import google.registry.request.Action;
 import google.registry.request.HttpException.BadRequestException;
 import google.registry.request.HttpException.NotFoundException;
@@ -51,6 +52,11 @@ public class RdapNameserverAction extends RdapActionBase {
     return "nameserver";
   }
 
+  @Override
+  public EndpointType getEndpointType() {
+    return EndpointType.NAMESERVER;
+  }
+
   @Override
   public String getActionPath() {
     return PATH;