Add save_on_exception option to ModelCheckpoint

[vsey]

What does this PR do?
This PR adds a save_on_exception option to the ModelCheckpoint callback. This some of this functionality is already implemented in the OnExceptionCheckpoint checkpoint, but I believe that bundling all checkpoint options in the ModelCheckpoint is more intuitive. Additionally, this leads to the same naming conventions and directory paths used for the exception checkpoint as for all the others.
When enabled, this option serves as a contingency in case of any disruption during training, allowing one to continue from the last step before the exception occurs without losing too much progress. By printing the exception type and message, this also alleviates issue #20187.

Fixes #19686

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📚 Documentation preview 📚: https://pytorch-lightning--20916.org.readthedocs.build/en/20916/