internal/postgres: log every DB query
internal/postgres: log every DB query

Log the start and end of every DB query.

Change-Id: If9d053c1ff409ef1ce1fd54ec35e79d24f2d8ab3
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/555198
Reviewed-by: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite