CLI tool to manipulate subscriptions in the database

[hanstrompert]

Problem to solve

In some cases it is necessary to manipulate subscriptions directly in the database. To make this a safe operation it would be nice to make these changes through a CLI tool. This makes sure we can do all necessary validation through the domain models.

E.g.:

python main.py update_subscription <subscription_id>

Intended users

Developers and operators.

Further details

• Document this feature, implement validation through domain model validators.
• Please make the command transactional, so that you need to make an explicit save.
• Make it possible to view a diff of the change that you would like to execute.