Event descriptions and metadata

[pauline1010]

To be able to use events in a more meaningful way, giving the user the relevant information.

[dmhv]

As @hulien22 explained on Slack, we can only display Type, Description and Tags (which are a Grafana thing, no relation to CDF, see docs) for a given event.

Example case: in Grafana, we can render a column as a URL, using some column values to construct a link. For instance, if we have alarm documentation pages sitting at www.base.url/doc/ALARM_TYPE, we can have the dynamic part (ALARM_TYPE) in one of those table columns, and create URLs pointing to specific pages relevant to each alarm. However, using either Type or Description for that in CDF seems suboptimal.

Proposed solution: it may be better to store the dynamic URL part in event metadata, and then within Grafana replace the Description column with the contents of the specified metadata field.

Example event metadata:
{'event_url': 'v1/pump/seal_failure'}

Example Grafana annotations query:
event{type="Down", assetSubtrees=[42], replaceDescription=True, replaceDescriptionKey='event_url'}