Feat:Wrap Openllm, Fireworks and other services into the OpenAILLM class.

[YangQianli92]

Features

• Wrapping OpenLLM, FireWorksAI,Moonshot services into OpenAILLM
• OpenLLM, FrreWorksAI, Moonshot will be registered in OpenAILLM class
• Removed OpenLLM and FireWorks class
• Provide a uniform method of calculating usage in OpenAILLM class
• Added support for MistralAI services

Feature Docs
Specific configuration documentation can be found in this PR
geekan/MetaGPT-docs#100

Unit Test
pytest tests/metagpt/provider/test_openai.py

============================= test session starts =============================
collecting ... collected 8 items

test_openai.py::test_text_to_speech 
test_openai.py::test_speech_to_text 
test_openai.py::TestOpenAI::test_make_client_kwargs_without_proxy 
test_openai.py::TestOpenAI::test_make_client_kwargs_with_proxy 
test_openai.py::TestOpenAI::test_get_choice_function_arguments_for_aask_code 
test_openai.py::TestOpenAI::test_aask_code_json_decode_error 
test_openai.py::test_gen_image 
test_openai.py::test_openai_acompletion 

======================= 8 passed, 8 warnings in 38.95s ========================
PASSED                               [ 12%]PASSED                               [ 25%]PASSED [ 37%]PASSED    [ 50%]PASSED [ 62%]2024-02-29 11:27:48.097 | INFO     | tests.metagpt.provider.test_openai:test_get_choice_function_arguments_for_aask_code:111 - 
test get function call arguments 0: {'language': 'python', 'code': "print('hello world')"}
2024-02-29 11:27:48.098 | INFO     | tests.metagpt.provider.test_openai:test_get_choice_function_arguments_for_aask_code:115 - code is : print('hello world')
2024-02-29 11:27:48.098 | INFO     | tests.metagpt.provider.test_openai:test_get_choice_function_arguments_for_aask_code:111 - 
test get function call arguments 1: {'language': 'markdown', 'code': 'Completed a python code for hello world!'}
2024-02-29 11:27:48.098 | INFO     | tests.metagpt.provider.test_openai:test_get_choice_function_arguments_for_aask_code:115 - code is : Completed a python code for hello world!
2024-02-29 11:27:48.099 | INFO     | tests.metagpt.provider.test_openai:test_get_choice_function_arguments_for_aask_code:111 - 
test get function call arguments 2: {'language': 'python', 'code': "print('hello world')"}
2024-02-29 11:27:48.099 | INFO     | tests.metagpt.provider.test_openai:test_get_choice_function_arguments_for_aask_code:115 - code is : print('hello world')
PASSED      [ 75%]
2024-02-29 11:27:48.112 | INFO     | tests.metagpt.provider.test_openai:test_aask_code_json_decode_error:128 - code is : print('hello world')
PASSED                                    [ 87%]PASSED                           [100%]I'm AI assistant
I'm AI assistant

[better629]

LGTM

[geekan]

LGTM