Add option to stop swallowing errors on callbacks.

Currently, Active Record will rescue any errors raised within
after_rollback/after_create callbacks and print them to the
logs. Next versions of rails will not rescue those errors anymore,
and just bubble them up, as the other callbacks.

This adds a opt-in flag to enable that behaviour, of not rescuing
the errors.
    Example:
      # For not swallow errors in after_commit/after_rollback
      config.active_record.errors_in_transactional_callbacks = true

[fixes #13460]