Improve engine supercharger parameters to allow manual gear shifting

Reposting this question form MV. JimStewart as idea.

The engine parameters that were added for supercharger definition are a good
start, but it currently only allows for a supercharger to shift automatically
based on altitude. We have multiple projects that have a supercharger where
the shift is pilot-controlled. On the surface it seems that it would be a
simply matter to give optional control of the supercharger shifting to an
event. Would this be possible to include? Ideally, we’d like events for shift
up, shift down, and gear set, along with SimVars to query.

Not very confident that this will get much consideration. But yes, I support
this idea 100%.

Honestly I’d be happy if they would make a 2-stage supercharger possible but I
though your suggestion was better.