[P-verylow] Worker metrics

[ribasushi]

Now that this is fully in production, it would be nice to have some insights into the http requests. Specifically:

• Count of requests ( HEAD / GET separately ) per time of day, perhaps 2xx vs 4xx/5xx as well
• Duration + Transferred bytes per request ( to build speed averages )

This is not critical for any day-to-day operation, the insights would be nice to have when things ramp up.

[dchoi27]

cc @vasco-santos @plwileverts, worth getting into the support initiative

[vasco-santos]

This would be cool to get to know more about R2 perf. We can gather logs from worker and get metrics from them

[ribasushi]

cc @travisperson, @ognots to track to potentially reuse worker for snap-off-r2 when ready.