Inactive consumers should be put offline

[magnetised]

Hibernated consumers should be put offline after some timeout, so replacing the process hibernation with process shutdown (without shape removal).

This will reduce memory usage to some subset of the defined shapes, the size of which will depend on the timeout duration.

Shapes which are part of a sub-query chain should remain active (but hibernated). The existing dependency structure would not survive the restart of one of its members. Shutting down and restarting shapes with dependencies can be part of later work.

[balegas]

we should move this out of scope for this task.