fix: terminate pgbouncer on compute suspend (#12153)

## Problem

PgBouncer does not terminate connections on a suspend:
https://github.com/neondatabase/cloud/issues/16282

## Summary of changes

1. Adds a pid file to store the pid of PgBouncer
2. Terminates connections on a compute suspend

---------

Co-authored-by: Alexey Kondratov <kondratov.aleksey@gmail.com>

compute_tools/src/http/routes/terminate.rs

@@ -26,7 +26,7 @@ pub(in crate::http) async fn terminate(State(compute): State<Arc<ComputeNode>>)
         drop(state);
     }
 
-    forward_termination_signal();
+    forward_termination_signal(false);
     info!("sent signal and notified waiters");
 
     // Spawn a blocking thread to wait for compute to become Terminated.