Fix improper shutdown

Run strapi in the background so we can catch signals and properly shutdown strapi.
Docker stop sends a SIGTERM which is ignored by strapi and causes Docker to kill the container (exit 137). This catches the SIGTERM and sends a SIGINT (CTRL-C) to strapi.
We cannot use STOPSIGNAL in the Dockerfile as SIGINT is a signal that will not be passed to PID 1 (which is the wrapper-script).

strapi.sh

@@ -1,6 +1,14 @@
 #!/bin/sh
 set -ea
 
+_stopStrapi() {
+  echo "Stopping strapi"
+  kill -SIGINT "$strapiPID"
+  wait "$strapiPID"
+}
+
+trap _stopStrapi SIGTERM SIGINT
+
 cd /usr/src/api
 
 APP_NAME=${APP_NAME:-strapi-app}
@@ -15,4 +23,7 @@ then
 fi
 
 cd $APP_NAME
-strapi start
+strapi start &
+
+strapiPID=$!
+wait "$strapiPID"