AR::RecordNotSaved & RecordNotDestroyed from save!/destroy! should include an error message

When calling `AR::Base.save!` or `AR::Base.destroy!` and raising one of the exceptions, give a meaningful error message so that people can easily understand why it's failing to save/destroy.

cc @arthurnn @rafaelfranca
Talking about callbacks is confusing here since it can fail to save due to validations. Maybe just `Failed to save the record`?