I'm asking a Grafana/Prometheus question on SU, and I could see there is a grafana tag, but not a prometheus tag. And it appears I need 300 rep to suggest a tag (it should be noted I have over 3500 rep on Ask Ubuntu).
I just did a search for some stats:
Search for Prometheus: 44 results, and does not have a tag.
InfluxDB is another popular data source for Grafana.
So based on these stats, I would sincerely suggest that a prometheus tag could be created. I would be willing to come up with tag description suggestions for both prometheus, influxdb, grafana and other related tags.