Add support for .aider.conf.yml to allow wider model provider selection

[philikai]

Would be great if we could add support for amazon bedrock, or simply using the .aider.conf.yml file that we have with the normal aider setup.

[AlexJ-StL]

I would also like to see something like this (ultimately with the goal of greater model support) and OP's suggestion about the use of .aider.conf.yml seems like a good suggestion from my view.