refactor dashboard action using template variables in grafana

refactor of grafana dashboard action:

• remove query of datastreams from dispatcher action
• remove db_url from main.py
• create multiple panels with variable templating datastream_pos and repeat panel option.

could be improved:

• panel query, getting the observations to the fitting datastream_pos values shoud probably done with a join on the datastream_id

Integration of dynamically created grafana dashboards into tsm-orchestration is done by orchestration MR tsm-orchestration!82 (merged)