Add a histogram metric for SQL requests

[fulmicoton]

Right now we do monitor the metastore grpc request time, but we do not have a metric measuring closely the time spent running postgresql requests.

We want an explicit (chosen, not generated from the SQL query) label for each sql client callsite too.

Also, the current histogram scale stops at 4s and it happens to not be enough. It would be better to go to 16s.

[PSeitz]

Related issue https://github.com/launchbadge/sqlx/issues/1896