L2SS-685: Add and configure Alerta SLACK & Grafana & LOFAR plugins

.gitignore

docker-compose/alerta-web/Dockerfile

docker-compose/alerta-web/README.md

docker-compose/alerta-web/alerta-secrets.json

docker-compose/alerta-web/alertad.conf

docker-compose/alerta-web/grafana-plugin/alerta_grafana.py

docker-compose/alerta-web/grafana-plugin/setup.py

docker-compose/alerta-web/lofar-plugin/alerta_lofar.py

docker-compose/alerta-web/lofar-plugin/setup.py

docker-compose/alerta-web/rules.json

docker-compose/alerta.yml

docker-compose/grafana/Dockerfile

docker-compose/grafana/README.md

docker-compose/grafana/grafana.ini

docker-compose/grafana/import-rules.py

docker-compose/grafana/rules.json

tangostationcontrol/docs/source/alerting.rst

tangostationcontrol/docs/source/index.rst

tangostationcontrol/docs/source/installation.rst