Avoid using root user for DB connection

[Barteus]

The user for MySQL connection is hardcoded as root. In the same relation, a user was created called mysql. Using root users for connections is not a good practice.

    related-units:
      mlflow-db/0:
        in-scope: true
        data:
          database: database
          egress-subnets: 100.98.244.78/32
          host: 100.98.244.78
          ingress-address: 100.98.244.78
          password: password
          port: "3306"
          private-address: 100.98.244.78
          root_password: root
          user: mysql

mlflow-operator/charms/mlflow-server/src/charm.py

Line 370 in 6d7b891

"MLFLOW_TRACKING_URI": f"mysql+pymysql://root:{mysql['root_password']}@{mysql['host']}"

[misohu]

Fixed in https://github.com/canonical/mlflow-operator/tree/KF-715-mlflow-v211 close after merge