docstr: Return a parser with arguments sourced from several sub models.
code: def get_additional_agent_args(cls) -> ParlaiParser:
      """
      Return a parser with arguments sourced from several sub models.
      """
      additional_agent_parser = SeekerAgent.get_additional_agent_args()
      GPT2ComboAgent.add_cmdline_args(additional_agent_parser)
      return additional_agent_parser
  
imports: from typing import Optional, Tuple, List, Union
  import torch
  import torch.nn
  from parlai.agents.fid.fid import FidModel, FidAgent, SearchQuerySearchEngineFiDAgent, WizIntGoldDocRetrieverFiDAgent
  from parlai.agents.hugging_face.gpt2 import Gpt2Agent
  from parlai.agents.rag.rag import BaseGenerationAgentMixin
  from parlai.agents.rag.retrievers import Document
  from parlai.core.dict import DictionaryAgent
  from parlai.core.message import Message
  from parlai.core.opt import Opt
  from parlai.core.params import ParlaiParser
  from parlai.core.torch_agent import Batch, Output
  from parlai.core.torch_generator_agent import TorchGeneratorAgent
  from parlai.utils.torch import padded_tensor
  from projects.seeker.agents.seeker import SeekerAgent
  from projects.seeker.agents.gpt2_seeker_modules import GPT2WithRetrieverModel, ComboGPT2Model
label_desc: Use image node_id 1 for calling the GPT2SeekerAgent obj's underlying member method code with example usage: obj.get_additional_agent_args(cls) and returns: additional_agent_parser