Support caching_sha2_password authentication

[leaf-potato]

Starting from MySQL 8.0, caching_sha2_password authentication is used by default, and mysql_native_password authentication is deprecated in MySQL 9.0. It may be better to support caching_sha2_password in opensrv.

Refer to: https://dev.mysql.com/doc/relnotes/mysql/9.0/en/news-9-0-0.html