Override max_epochs on resume from checkpoint with SSR

[ajaysaini725]

When resuming from a checkpoint, max_epochs currently defaults to the original max_epochs which prevents users from being able to train for more than the original max_epochs when resuming from a checkpoint.

It would be good to be able to resume from checkpoint and train for more epochs than the original max_epochs. However, we need to come up with a scheme to make this work with scale_schedule_ratio because scale schedule ratios are computed assuming that max_epochs does not change.

How should we go about handling this?

[ravi-mosaicml]

Fixed via #445....the SSR and max duration are not persisted in a checkpoint, so whatever values are passed to the trainer upon checkpoint resume will be used.