Allow model credentials to be stored in an .env file

[jwmatthews]

Consider moving to our model coordinates (sensitive) information being stored in a python dotenv file and/or determined from environment.

https://pypi.org/project/python-dotenv/

Related to #85

[JonahSussman]

I think the key is automatically loaded from the environment if it is present. I'm looking at https://github.com/konveyor-ecosystem/kai/blob/6049eff2ea1b74d68c75554e8854302100322340/kai/model_provider.py#L47-L52 and https://github.com/konveyor-ecosystem/kai/blob/6049eff2ea1b74d68c75554e8854302100322340/kai/model_provider.py#L105-L113 OpenAI's key check still needs to be implemented if we want, but langchain does that for us

[jwmatthews]

Removed the priority on this. It's not essential to demo flow, usage of environment variables is fine for now.

[fabianvf]

Configuration IDE side has matured to the point that this issue is obsolete