*) revert executor wait queue size comparison. This is too
aggresive and with stall check below, now unnecessary.
*) new container logic now checks if stats are constant, if
this is the case, then we assume the system is stalled (eg
running functions that take long time), this means we need
to make progress and spin up a new container.
*) during shutdown, errors should be 503
*) new inactivity time out for hot queue, we previously kept hot queues in memory forever.
*) each hot queue now has a hot launcher to monitor and launch hot containers
*) consumers now create a consumer channel with startDequeuer() that can be cancelled via context
*) consumers now ping (signal) hot launcher every 200 msecs until they get a slot
*) tests for slot queue & mgr
