Move decider_client_from_config() back to reddit_decider dir

[mrlevitas]

I was able to import from reddit_decider import decider_client_from_config with version v1.0.3-alpha (prior to this update) in experiment-config server so I'm moving this fn back with the rest of decider stuff.

[wuyiqicc]

The thing is that developers integrate, do they have to import both reddit-decider and reddit-experiments? It is a bit confusing not to put the interfaces together.

[mrlevitas]

The thing is that developers integrate, do they have to import both reddit-decider and reddit-experiments? It is a bit confusing not to put the interfaces together.

Just the latter package (reddit-experiments, this sdk) is required for devs.
reddit-decider is a dependency of this sdk and will get pulled in, but that's not the same as what we're importing here via from reddit_decider import decider_client_from_config.
reddit_decider in the import statement is the module (i think that's the correct term) within reddit-experiments package.