Fix autoresume with non-default CheckpointSaver.

[aadyotb]

What does this PR do?

This PR fixes a bug where autoresumption fails when specifying a custom CheckpointSaver that saves to a remote folder. The bug occurs because when attempting to autoresume, Trainer, will look at self._checkpoint_saver.folder; however this is set to a local path, instead of the remote path:

composer/composer/callbacks/checkpoint_saver.py

Line 294 in 4ae29b1

self.folder = local_folder

This PR adds a check for a remote folder in the checkpoint saver to resolve the issue.

What issue(s) does this change relate to?

Fixes: #3902

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