code: def set_identifier(
      self, message_identifier: PostgresBackendMessageIdentifier
  ):
      self.identifier = message_identifier.value
      return self
  
imports: import struct
  from typing import List, Any, BinaryIO, Sequence, Dict
  from mindsdb.api.postgres.postgres_proxy.utilities import strip_null_byte
  from mindsdb.utilities import log
  import time
  from mindsdb.api.postgres.postgres_proxy.postgres_packets.postgres_fields import PostgresField
  from mindsdb.api.postgres.postgres_proxy.postgres_packets.postgres_message_identifiers import PostgresBackendMessageIdentifier, PostgresFrontendMessageIdentifier, PostgresAuthType
label_desc: Use image node_id 3 for calling the PostgresPacketBuilder obj's underlying member method code with example usage: obj.set_identifier(message_identifier) and returns: self