Returns a list of MetricMetadata for communicator-related metrics.

def GetMetricMetadata():
  """Returns a list of MetricMetadata for communicator-related metrics."""
  return [
      stats_utils.CreateCounterMetadata("grr_client_unknown"),
      stats_utils.CreateCounterMetadata("grr_decoding_error"),
      stats_utils.CreateCounterMetadata("grr_decryption_error"),
      stats_utils.CreateCounterMetadata("grr_authenticated_messages"),
      stats_utils.CreateCounterMetadata("grr_unauthenticated_messages"),
      stats_utils.CreateCounterMetadata("grr_rsa_operations"),
      stats_utils.CreateCounterMetadata(
          "grr_encrypted_cipher_cache", fields=[("type", str)]),
  ]