Provide an interface to perform the PostgreSQL database migration

As a user, I would like to have a simple way to upgrade my database. Ideally, there should be a message that informs me about migration and starts it when I click on the "Start migration" button.

As a developer, I would like users to be blocked for any action during the migration process.

depends on: https://github.com/aiidateam/aiida-prerequisites/issues/41