Add traffic metrics

[MadLittleMods]

Add traffic metrics to see how many people are using it.

Do we need to add anything special to make this happen? Can we already derive this information from some existing metrics we get from K8s? Perhaps the nginx/nginx-ingress-controller dashboards (example)

Should we derive this info from the response metrics? #45 (also see that issue for Prometheus notes)

[MadLittleMods]

Can we already derive this information from some existing metrics we get from K8s? Perhaps the nginx/nginx-ingress-controller dashboards (example)

The reasoning below is for the matrix.org site, not archive.matrix.org but the reasoning is the same on why the nginx dashboards aren't enough:

Since the website is cached by CF [(Cloudflare)], [nginx] cannot give meaningful metrics

The CF dashboard can give us the number of hits per page and the Top 15 pages visited according to filters, which is acceptable for now

-- matrix-org/matrix.org#1785 (comment)