Add option to stop swallowing errors on callbacks.

The current behaviour is to only log errors that happen on
`after_commit` and `after_rollback` callbacks, this commit adds a
option to active record which make those errors actually raise instead
of only be logged.
    Example:

        # For not swallow errors in after_commit/after_rollback callbacks.
        config.active_record.raise_in_transactional_callbacks = true

The option should be removed in future versions of Rails, as the desired
behaviour is not to swallow exceptions.

[fixes #13460]