Factor METMaker algs from METAssociation config

This is a minor adjustment to the "new" (ComponentAccumulator-based) MET configuration code to separate out two different pieces that don't need to be tied together. Currently, configuring the MET association algorithms also schedules METMaker algorithms, which isn't always desirable. In the derivation framework for example, we want to only save the output of the association algorithm and not the final MET object itself (which should always be constructed at analysis level), so this would be a waste of resources.

This should have no impact on the behavior of any existing code, it's only intended to allow more flexibility in the future.

Tagging @williams, @schaarsc, @sawyer, @khoo for their awareness.