First event number should always be 1 or larger. This makes sure event selectors respect that.
Also update all default configuration to use 1 instead of 0.
Let me know if this needs to be discussed at the Core SW or SW coordination, but it was already decided at the OAB meeting when discussing MC21 production that no events should have event number of 0.
This fixes on-the-fly generation in simulation jobs, but also some other test/convenience scripts.