Enhancement: Create account and asset via API

[ArdJonker]

To make the configuration easy for the user and to have less administration for the admin of FM it would be helpful if the user can create an account and asset from V2G Liberty in the configuration flow.

The account should be marked as "has not paid yet" so it will not receive smart schedules yet. Admin should be able to edit this later.

Maybe this should be an plug-in for FM?

[Flix6x]

After a discussion we settled on first developing towards supporting asset and sensor creation via the API, and with it, a script that can be run to set up a new site (e.g. one set up for V2G) through API calls.

The new account and user still need to be set up by the FlexMeasures host through the CLI.

This means the new site will first be set up under the account of the API user (e.g. you), and you can subsequently ask your host (e.g. us) to move the asset over to the new user's account, for example, after a subscription has been arranged.