WL#11143: Change default log_error_verbosity to 2

Affects: Server-8.0   —   Status: Complete   —   Priority: Medium

Change default log_error_verbosity from 3 (Notes) to 2 (Warning).

The purpose is to make MySQL 8.0 less verbose by default.

https://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_log_error_verbosity