Logger-specific checkpoint callbacks
🚀 Feature
Add checkpoint callbacks corresponding to each logger.
Motivation
Recently, PL supports a lot of loggers like comet.ml, eptune.ai or etc. Many of them have the functionality to store the weight files on their cloud storage, however, PL has logging and checkpointing features independently. The loggers also have automatic detection of the checkpoints and upload them, however, it is difficult to interpret PL's high-level wrapping completely. In this situation, we cannot fully benefit from the loggers.
Pitch

Adding checkpoint callbacks corresponding to each logger. e.g. CometLogger - CometCheckpoint.

Alternatives
I think it is possible with small changes of save_function because TrainerCallbackConfigMixin has already had the logger object as a member. The specific usage should be investigated in each community.