feat(provisioners): added default mysql provisioner

[astromechza]

This copies the existing postgres provisioner and adapts it for mysql.

This was tested with a score file that looks like:

apiVersion: score.dev/v1b1
metadata:
    name: demo-app
containers:
    main:
        image: ghcr.io/astromechza/demo-app:v0.6.1
        variables:
            OVERRIDE_MYSQL: ${resources.db.username}:${resources.db.password}@tcp(${resources.db.host}:${resources.db.port})/${resources.db.name}
service:
    ports:
        web:
            port: 8080
resources:
    db:
        type: mysql

Which correctly verified that the database DSN for mysql was valid and connected ok.

Unlike score-compose, this provisioner uses a single database per instance model - which is generally ok for the moment as a proof of concept and providing some basic support.

Fixes #13 .

[mathieu-benoit]

LGTM, thanks!