Related to: https://github.com/neondatabase/neon/issues/2848
`pageserver_storage_operations_seconds` is the most expensive metric we
have, as there are a lot of tenants/timelines and the histogram had 42
buckets. These are quite sparse too, so instead of having a histogram
per timeline, create a new histogram
`pageserver_storage_operations_seconds_global` without tenant and
timeline dimensions and replace `pageserver_storage_operations_seconds`
with sum and counter.
Co-authored-by: Joonas Koivunen <joonas@neon.tech>
20b38acff0