improve: Use opstatlogger for recording more details of reading from db ledger

[ethqunzhong]

Motivation

In order to more accurately observe the latency distribution of reading entries from the db ledger storage engine (includes: read_locations_index, read_entrylog, readahead)

Changes

read_locations_index, read_entrylog, and readahead metrics types are adjusted from Counter to OpStatsLogger.

Adjustment before and after as follows