default log store backend to WAL and allow disabling verification

[dhiaayachi]

Description

This PR change the default log store config to use WAL when starting with a fresh database. If a bolt db already exist bolt db will be used as a backend and a warning will be logged.

It also allow the log verifier, enabled by default, to be disabled.

Testing & Reproduction steps

Added tests to verify combination of configs.

PR Checklist

• [x] updated test coverage
• [x] external facing docs updated
• [x] appropriate backport labels added
• [x] not a security concern