/stats endpoint

[gmelodie]

We should have a way to get stats from autoretrieve. The ones I'd personally like are:

• when was the last successful estuary heartbeat
• was the last estuary heartbeat failed?
• how many retrievals we did in the last hour

Not sure if we already have something like this

[rvagg]

We don't, not directly from autoretrieve anyway. But when plugged into a prometheus backend we get a ton of stats, as of this week's changes we're even down to getting specifics on errors:

I imagine it wouldn't be too hard to get something similar set up for Estuary's autoretrieve instance and adding in those additional heartbeat metrics wouldn't be hard (see this week's changes for examples).