Add a composition time stepper

[GiudGiud]

Reason

Sometimes we want to benefit from the behavior of multiple time steppers, but save for re-implementing what s missing (for example IterationAdaptiveDT did that), you cant mix & match

Tied to #8127 and #3858

Design

• allow timestepper action to create multiple timesteppers (force the selection of one if multiple)
• add a composition rule time stepper that can call the others
  max step, min step, average of steppers' step, times to hit absolutely (or with a tolerance?), periods of validity for each composed stepper etc

The periods of validity could be a parameter of each stepper instead

This would be a lot less intrusive than the Stepper system designed by @friedmud in #8127

Impact

Reaching full & final capability for time steppers?

[MengnanLi91]

@GiudGiud I can work on this

[friedmud]

Yeah - I like this. Now that we've done this a few times with sub-Generators, etc... I think we know that this pattern works pretty well.