Network Dashboard: Make container stop on SIGTERM

The Docker Compose file specifies a shell script for the container entrypoint. This is necessary (at least as long as we don't use templates; see comment in `docker-compose.yaml` right above the changed line) to set up redirection for the calls to Collector Backend.

The script ends with a call to the native nginx entrypoint script. But apparently, the script running in the context of a plain shell means that SIGTERM is ignored. With this change, the entrypoint script is now invoked with `exec` which replaces the process and eliminates the problem.

network-dashboard/docker-compose.yaml

@@ -48,6 +48,6 @@ services:
       EOF
       # It also looks like the entrypoint scripts come with the ability to build the config from a template
       # (check out '/docker-entrypoint.d/20-envsubst-on-templates.sh').
-      /docker-entrypoint.sh nginx -g 'daemon off;'
+      exec /docker-entrypoint.sh nginx -g 'daemon off;'
     ports:
     - "${NETWORK_DASHBOARD_PORT-8080}:80"