Right now the plugin API provides two main callbacks for the transaction flow, resolved() and transaction(). Unfortunately, there are cases where they are not enough. I was looking into improving the snapper plugin so that it takes properly labelled snapshots before and after a transaction runs, but resolved() runs before the user is prompted for confirmation, and therefore is not a good place to take the snapshot.

I would like if a pre_transaction() hook existed that fired right after the transaction is already confirmed but before it is executed. So the flow would end up like this:

- dnf starts, processes command line, resolves deps
- resolve() is called
- user is prompted for confirmation, transaction integrity is verified
- pre_transaction() is called
- transaction is run
- transaction() is called