Unify metric rate limiting

[Dav1dde]

Sessions currently run through the rate limiting code, but the moment they are converted to metrics they are no longer considered for rate limiting. This is not an issue as they were designed to be never need rate limiting and ingestion can still be disabled with a 0 quota.

But ideally we unify all our code in Relay, the code which takes items and generates metrics out of them, the metrics then should carry on the outcomes as well as the rate limits of the original item.

[linear[bot]]

RELAY-164