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>

test_runner/fixtures/neon_cli.py

@@ -564,6 +564,7 @@ class NeonLocalCli(AbstractNeonCli):
         basebackup_request_tries: int | None = None,
         timeout: str | None = None,
         env: dict[str, str] | None = None,
+        dev: bool = False,
     ) -> subprocess.CompletedProcess[str]:
         args = [
             "endpoint",
@@ -589,6 +590,8 @@ class NeonLocalCli(AbstractNeonCli):
             args.extend(["--create-test-user"])
         if timeout is not None:
             args.extend(["--start-timeout", str(timeout)])
+        if dev:
+            args.extend(["--dev"])
 
         res = self.raw_cli(args, extra_env_vars)
         res.check_returncode()