Upgrade

[ichvets (ivan chvets)]

Upgrade guides:

• Upgrade Charmed Kubeflow from 1.4 to 1.6
• Upgrade Charmed Kubeflow from 1.6 to 1.7
• Upgrade Charmed Kubeflow from 1.7 to 1.7 Patch 1
• Upgrade Charmed Kubeflow from 1.7 to 1.8

Database migration guides:

• MariaDB - MySQL Databases Migration Guide