Migrate to Sentry Uptime Monitors

[JacobCoffee]

https://sentry.io/product/uptime-monitoring/

Would save ~$45/mo on Pingdom? @ewdurbin

[ewdurbin]

We don’t pay for pingdom, but consolidation would be nice! Also consider https://docs.datadoghq.com/synthetics/

I have ported some of our pingdom check’s there over time as a tests