chg: [compose] provide ``$HOST_COMPOSE_LAUNCHER_OPTS`` in environment

Indeed, without this, charms can't access the real content of the file.

Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>

bin/compose

@@ -933,6 +933,7 @@ mk_docker_run_options() {
     dest="/var/lib/compose/sessions/$UID-$hash"
     additional_docker_run_opts=(
         "-v" "$SESSION_DIR/$UID-$hash:$dest:ro"
+        "-e" "HOST_COMPOSE_LAUNCHER_OPTS=$SESSION_DIR/$UID-$hash"
         "-e" "COMPOSE_LAUNCHER_OPTS=$dest"
         "-e" "COMPOSE_LAUNCHER_BIN=$COMPOSE_LAUNCHER_BIN"
     )