Allow choice of Keyring to be configured in YAML

This uses a Dagger-provided map of Keyring implementations, with two currently available,
"KMS" and "Dummy". The active keyring is configured in the YAML file, so we no longer
require MOE directives to choose which one to use for internal/external builds.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=216898058

java/google/registry/keyring/kms/KmsModule.java

@@ -19,13 +19,23 @@ import com.google.api.services.cloudkms.v1.CloudKMS;
 import dagger.Binds;
 import dagger.Module;
 import dagger.Provides;
+import dagger.multibindings.IntoMap;
+import dagger.multibindings.StringKey;
 import google.registry.config.CredentialModule.DefaultCredential;
 import google.registry.config.RegistryConfig.Config;
+import google.registry.keyring.api.Keyring;
 
-/** Dagger module for Cloud KMS connection objects. */
+/** Dagger module for Cloud KMS. */
 @Module
 public abstract class KmsModule {
 
+  public static final String NAME = "KMS";
+
+  @Binds
+  @IntoMap
+  @StringKey(NAME)
+  abstract Keyring provideKeyring(KmsKeyring keyring);
+
   @Provides
   static CloudKMS provideKms(
       @DefaultCredential GoogleCredential credential,