Expose encrypted data from the keyring

This makes it possible to request the encrypted data directly in application code. It will be used to download service account credential during "nomulus login".

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=222847905

java/google/registry/keyring/api/Keyring.java

@@ -156,6 +156,12 @@ public interface Keyring extends AutoCloseable {
    */
   String getJsonCredential();
 
+  /**
+   * Returns the encrypted data for the given key name. Only use this method when decryption is not
+   * required.
+   */
+  String getEncryptedData(String keyName);
+
   // Don't throw so try-with-resources works better.
   @Override
   void close();