Similar to the new Tasks, Schedule runspaces should be cleaned-up after they're complete

[Badgerati]

A quick last minute addition to v2.6.0. When I added Task support I made it so the runspaces used would be cleaned-up once the Task has completed - to free up resources.

Schedule runspaces aren't having this occur, and similar to Tasks, once they're complete they should be disposed and removed.

[Badgerati]

I've added a [GC]::Collect() to occur when the server closes, or is restarted - just to help free up resources.

I have other ideas about using GC in other parts of Pode which I need to further explore, but I'll save it for one of the next releases (2.6.1 or 2.7.0) - once I can test it and write it up.