(possibly temporary) fix for #18519
Matches OpenSSH for non-tty sessions, where we don't actively terminate
the process.
Adds explicit tracking to the SSH server for these processes so that if
we are shutting down we terminate them: this ensures that we can shut
down quickly to allow shutdown scripts to run. It also ensures our tests
don't leak system resources.
Fix hanging workspace shutdowns caused by orphaned SSH child processes.
Key changes:
- Create process groups for non-PTY SSH sessions
- Send SIGHUP to entire process group for proper termination
- Add 5-second timeout to prevent indefinite blocking
Fixes#17108