Set config values in the grafana.ini that's stored in the persistent-config directory

Currently the docker-launcher.sh script. Only works on first load when grafana-config-bootstrap-done-marker is not set, but it only writes the config to /etc/grafana/grafana.ini which is just on the docker image. So on a subsequent redeploy the docker-launcher.sh sees the sentinel file and does not make the config changes and we just get the default config file.

This change will copy the default /etc/grafana/grafana.ini file to the /etc/pgwatch2/persistent-config dir and makes the changes there. Then it will copy over that file to /etc/grafana/grafana.ini at startup, preserving the config changes.