ssh: launch new tmux session in group "ssh" after connecting

supersedes https://git.hammerle.me/fphammerle/setup/commit/d87a42de49cbefcd9436b10b542769d8aaecf414

config.rasi

@@ -1,5 +1,5 @@
 configuration {
 	/* --hold supported by termite & kitty */
-	ssh-command: "{terminal} --hold -e {ssh-client} {host} [-p {port}]";
+	ssh-command: "{terminal} --hold -e {ssh-client} -t [-p {port}] {host} exec tmux new-session -t ssh";
 	combi-modi: "drun,ssh,run,password-store-type:~/.config/rofi/scripts/password-store-type";
 }