Update MySQL creation

Updating MySQL account creation to use SHA2 instead of MD5 hashing, this is now the standard on MySQL 8.0+.

Related to: https://gitlab.cern.ch/wordpress/infra-planning/-/issues/52

DBoD Reference: https://dbod-user-guide.web.cern.ch/instance_management/upgrading/MySQL/mysql_8_4/#reasoning-for-changing-to-caching_sha2_password

Notes:

Important: This change is not backwards compatible, pushing this version of the operator would require changes to the existing secrets.