Update output format of MosaicML endpoint to be more flexible

[dakinggg]

There will likely be another change or two coming over the next couple weeks as we stabilize the API, but putting this one in now which just makes the integration a bit more flexible with the response output format.

(langchain) danielking@MML-1B940F4333E2 langchain % pytest tests/integration_tests/llms/test_mosaicml.py tests/integration_tests/embeddings/test_mosaicml.py 
=================================================================================== test session starts ===================================================================================
platform darwin -- Python 3.10.11, pytest-7.3.1, pluggy-1.0.0
rootdir: /Users/danielking/github/langchain
configfile: pyproject.toml
plugins: asyncio-0.20.3, mock-3.10.0, dotenv-0.5.2, cov-4.0.0, anyio-3.6.2
asyncio: mode=strict
collected 12 items                                                                                                                                                                        

tests/integration_tests/llms/test_mosaicml.py ......                                                                                                                                [ 50%]
tests/integration_tests/embeddings/test_mosaicml.py ......                                                                                                                          [100%]

=================================================================================== slowest 5 durations ===================================================================================
4.76s call     tests/integration_tests/llms/test_mosaicml.py::test_retry_logic
4.74s call     tests/integration_tests/llms/test_mosaicml.py::test_mosaicml_llm_call
4.13s call     tests/integration_tests/llms/test_mosaicml.py::test_instruct_prompt
0.91s call     tests/integration_tests/llms/test_mosaicml.py::test_short_retry_does_not_loop
0.66s call     tests/integration_tests/llms/test_mosaicml.py::test_mosaicml_extra_kwargs
=================================================================================== 12 passed in 19.70s ===================================================================================

Who can review?

@hwchase17
@dev2049

[hwchase17]

thanks!