@CanIgnoreReturnValue
  public synchronized KeysetManager add(KeyTemplate keyTemplate) throws GeneralSecurityException {
    addNewKey(keyTemplate.getProtoMaybeThrow(), false);
    return this;
  }
Generates and adds a fresh key generated using {@code keyTemplate}.

@throws GeneralSecurityException if cannot find any {@link KeyManager} that can handle {@code
    keyTemplate}
java_src/src/main/java/com/google/crypto/tink/KeysetManager.java