With the current implementation, only the first call to `waitForShutdown` on a given
`ShutdownLatch` will return, while others will block (typically indefinitely). That's not
how one would expect a shutdown latch to work.
This isn't currently a concrete issue because we only wait once on each `ShutdownLatch`.
But in the context of #4154 we'll probably end up wanting to wait for shutdown from
multiple threads.
This adds a number of tests to verify the current behaviour, and adds a test for multiple
`waitForShutdown` calls that fails prior to the functional change.
PR-URL: https://github.com/hasura/graphql-engine-mono/pull/4162
GitOrigin-RevId: 9a108858d11390b847404f30bc7b93c06fc3f966
