AppShutdownStrategy

There are two possible graceful termination paths for an application:

1. User explicitly calls AppShutdownStrategy#releaseAwaitLatch

2. The application received SIGINT and the shutdown hook triggers.

   It's important to remember that all other threads will continue to run until the shutdown hook finishes, after that they'll stop abruptly without even receiving any exceptions.

   Izumi runtime will call AppShutdownStrategy#finishShutdown when all the cleanups are done.

Possible code paths:

1. AppShutdownStrategy#awaitShutdown -> AppShutdownStrategy#releaseAwaitLatch -> AppShutdownStrategy#finishShutdown
2. AppShutdownStrategy#awaitShutdown -> AppShutdownStrategy#finishShutdown