Refactor Demo to use Provisioning

[HadesArchitect]

see https://github.com/HadesArchitect/GrafanaCassandraDatasource/blob/main/docs/provisioning.md

1. Launch demo
2. Export dashboards as yaml configs
3. describe connection as a provisioning config
4. Remove grafana.db (preferably from git history too)
5. Test demo with provisioning

Theoretically should fix #209