[air] Do not warn of checkpoint_dir if it's coming from us (base_trainer).

[xwjiang2010]

Why are these changes needed?

Currently, the following information will be printed even the user is not directly using a tune function. This is confusing and not actionable.

 "`checkpoint_dir` in `func(config, checkpoint_dir)` is "
                    "being deprecated. "
                    "To save and load checkpoint in trainable functions, "
                    "please use the `ray.air.session` API:\n\n"
                    "from ray.air import session\n\n"
                    "def train(config):\n"
                    "    # ...\n"
                    '    session.report({"metric": metric}, checkpoint=checkpoint)\n\n'
                    "For more information please see "
                    "https://docs.ray.io/en/master/ray-air/key-concepts.html#session\n"

The new logic check if base_trainer is in the call stack and only adds the warning message when it is not. The new logic will be removed once internally we migrate to use session API.

Related issue number

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• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
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[krfricke]

This is a bit hacky. Can we just add a flag to wrap_function to not warn or alternatively just trigger log_once("tune_checkpoint_dir_deprecation") in our trainers?

[xwjiang2010]

This is a bit hacky. Can we just add a flag to wrap_function to not warn or alternatively just trigger log_once("tune_checkpoint_dir_deprecation") in our trainers?

Good point! Updated to warn=False in base_trainer