apps/lib: add a helper class for abort signals handling
apps/lib: add a helper class for abort signals handling

Seastar-style helper class that allows easy waiting for SIGINT/SIGTERM signals
from your app.

Example:

int main() {
...
seastar::thread th([] {
   seastar_apps_lib::stop_signal stop_signal;
   <some code>
   stop_signal.wait().get();  // this will wait till we receive SIGINT or SIGTERM signal
});

Signed-off-by: Vlad Zolotarov <976c0f8d0852ed6439ad273880b400a75a7c41d0@scylladb.com>

avikivity/seastar,syuu1228/seastar,avikivity/seastar,cloudius-systems/seastar,syuu1228/seastar,cloudius-systems/seastar,syuu1228/seastar,scylladb/seastar,dreamsxin/seastar,scylladb/seastar,scylladb/seastar,dreamsxin/seastar,dreamsxin/seastar,cloudius-systems/seastar,avikivity/seastar