Add way to pass in api keys to client

[PCSwingle]

I think the best way to use Spice will definitely be to just have a .env, but for people who want to pass in specific api keys, how should we handle this? We could just have them pass in an env dictionary to the client, but that is slightly confusing since we wouldn't actually be changing the environment variables.

[biobootloader]

passing in a dict is good I think. Can call it api_variables or something and say it takes precedence over what's found in the env