build Grafana and Prometheus images on CI
Created by: slimsag
This PR begins building the docker-images/grafana
and docker-images/prometheus
on CI.
They are published using the same versioning as Sourcegraph, per https://github.com/sourcegraph/sourcegraph/issues/9251
In specific, it is worth noting:
grafana and prometheus DO have version conflicts with traditional Sourcegraph versioning, but their version numbers started at 10.x.x so luckily we won't have any conflicts until years from now (at which point it seems fine to delete said old images).
Once merged, these images will auto-update and deploy nicely like all of our other images.