Abstract KMS code with KmsConnection and create a fake KmsConnection

This simplifies the tests for KmsKeyring and KmsUpdater.

This is a followup to []

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=148496758

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

@@ -39,4 +39,9 @@ public final class KmsModule {
         .setApplicationName(projectId)
         .build();
   }
+
+  @Provides
+  static KmsConnection provideKmsAdapter(KmsConnectionImpl kmsAdapter) {
+    return kmsAdapter;
+  }
 }