Merge branch 'L2SS-359-add-grafana' into 'master'

.gitmodules

docker-compose/grafana.yml

docker-compose/grafana/Dockerfile

docker-compose/grafana/dashboards/lofar2.0-station.json

docker-compose/grafana/dashboards/version-information.json

docker-compose/grafana/data_sources/aa

docker-compose/grafana/data_sources/ab

docker-compose/prometheus.yml

docker-compose/prometheus/Dockerfile

docker-compose/prometheus/prometheus.yml

docker-compose/tango-prometheus-exporter.yml

docker-compose/tango-prometheus-exporter/Dockerfile

docker-compose/tango-prometheus-exporter/LICENSE

docker-compose/tango-prometheus-exporter/Makefile

docker-compose/tango-prometheus-exporter/README

docker-compose/tango-prometheus-exporter/get_metrics.sh

...pose/tango-prometheus-exporter/ska-tango-grafana-exporter