Fix NPE in registry_tool when creating or updating a TLD with a dns writer

I forgot to inject the CreateTldCommand/UpdateTldCommand commands, which now
need to be injected so that the list of available DnsWriter implementations is
instantiated. This CL also adds a new DI Set<String> with just the name of the
writer, so that the instantiated writer map (which may have many DI dependencies)
doesn't need to be pulled in.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=130042215

java/google/registry/dns/writer/VoidDnsWriterModule.java

@@ -17,7 +17,9 @@ package google.registry.dns.writer;
 import dagger.Module;
 import dagger.Provides;
 import dagger.multibindings.IntoMap;
+import dagger.multibindings.IntoSet;
 import dagger.multibindings.StringKey;
+import javax.inject.Named;
 
 /** Dagger module that disables DNS updates. */
 @Module
@@ -26,7 +28,14 @@ public final class VoidDnsWriterModule {
   @Provides
   @IntoMap
   @StringKey(VoidDnsWriter.NAME)
-  static DnsWriter provideVoidDnsWriter(VoidDnsWriter writer) {
+  static DnsWriter provideWriter(VoidDnsWriter writer) {
     return writer;
   }
+
+  @Provides
+  @IntoSet
+  @Named("dnsWriterNames")
+  static String provideWriterName() {
+    return VoidDnsWriter.NAME;
+  }
 }