docker: ask s6 to stop all service when gitea stop (#9171)

* fix: ask s6 to stop all service when gitea stop

https://github.com/just-containers/s6-overlay#writing-an-optional-finish-script

* change service folder

docker/root/etc/s6/gitea/finish

@@ -1,2 +1,2 @@
 #!/bin/bash
-exit 0
+s6-svscanctl -t /etc/s6/