fix: update MySQL user creation for MySQL 8.0+ compatibility

[henribon]

Description

Fixes MySQL user creation script to be compatible with MySQL 8.0+.

Problem

The current user.sql uses deprecated syntax that fails on MySQL 8.0+:

GRANT ALL PRIVILEGES ON petclinic.* TO 'petclinic'@'%' IDENTIFIED BY 'petclinic';

Error message:

ERROR 1064 (42000): You have an error in your SQL syntax; 
check the manual that corresponds to your MySQL server version 
for the right syntax to use near 'IDENTIFIED BY 'petclinic'' at line 1

Solution

Updated to MySQL 8.0+ standard syntax following official documentation:

Fixes #2112