Unify naming of NSW simulation outputs and metadata with the rest of the muon subdetectors

I hope that this one will not be too intrusive, but it needs to be done before MC21 production starts. It fixes two items of the NSW naming:

• NSW HIT container names (sTGC/MMSensitiveDetector to sTGC/MM_Hits like for the other muon components)
• MM flag names as this is used for metadata generation (all other flags are acronyms)

While doing it I also added support to the ISF_CollectionMerger.

Note that this MR only keeps digi compatibility, everything else is renamed!

Keeping Draft for now to allow a bit more testing. Running full-integration-tests and full-unit-tests already (at least some references will have to be updated).

/cc @chchau @jojungge @rosati @pscholer @jchapman @stavrop @alaurier @tlari