CVE-2021-21328: Vapor's Metrics integration could cause a system drain

This is a DoS attack against anyone who Bootstraps a metrics backend for their Vapor app with the following attack vector:

1. send unlimited requests against a vapor instance with different paths. this will create “unlimited” counters and timers, which will eventually drain the system.
2. downstream services might suffer from this attack as well by being spammed with error paths