Add config for prometheus+grafana to mugwump, served at metrics.gws.fyi
with an Acme SSL cert.
Change-Id: Icc22b5079a24edbc4469233e938f926d92f63eb3
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2024
Reviewed-by: glittershark <grfn@gws.fyi>
Tested-by: BuildkiteCI