swh-alter: run tmux in a way that is compatible with bullseye

apps/swh-alter/entrypoint.sh

@@ -3,4 +3,9 @@
 set -e
 
 echo "swh-alter pod: running a tmux server"
-exec tmux -D
+tmux set -g exit-empty off \; start
+
+trap "tmux kill-server" INT TERM EXIT
+
+while tmux list-sessions 2>/dev/null; do sleep 5; done
+echo "tmux server has exited, bailing"