[tune] Log a deprecation warning for local_dir and related environment variables

[justinvyu]

Why are these changes needed?

Log a deprecation warning if a user sets RunConfig(local_dir), or either of the legacy RAY_AIR_LOCAL_CACHE_DIR or TUNE_RESULT_DIR environment variables.

For the migration period before passing in local_dir raises a deprecation warning, pass through local_dir to set storage_path if that is not set.

This PR also removes the remaining dependency on RAY_AIR_LOCAL_CACHE_DIR. The usage in Tune / RLlib is for running a Trainable manually, outside of Tuner.fit, where a logger will now have its default directory set to a folder within DEFAULT_STORAGE_PATH. The difference is that this is now no longer configurable via env vars, but the manual trainable use case is not a common pattern and use mainly used for debugging purposes.

Related issue number

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  • I've added any new APIs to the API Reference. For example, if I added a
    method in Tune, I've added it in doc/source/tune/api/ under the
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[matthewdeng]

@sven1977 could you PTAL at the RLlib change? Thanks!

[sven1977]

Approved from RLlib side.