Project inscription info

In this merge request, we add two new attributes to EnergyServiceApiInfo schema to check if a service has open inscriptions and also the URL of the form to join to that service.

Also, we develop a little refactor in energy_selfconsumption module, literals "active" and "inactive" are now constants ACTIVE and INACTIVE. This change is because we can use these literals in other modules, like `energy_communities_api.

{
    "address": {
        "city": "Barcelona",
        "country": "Spain",
        "postal_code": "08042",
        "state": "Barcelona",
        "street": "C/ Marie Curie 8",
        "street2": ""
    },
    "has_monitoring": true,
    "id_": 64,
    "inscription_date": null,
    "inscriptions": 2,
    "inscriptions_url_form": "http://odoo-ec.local:8069/inscription-data?model_id=64",
    "name": "instalaci\u00f3 Arkenova",
    "open_inscriptions": true,
    "power": 15.0,
    "shares": null,
    "status": "active",
    "type_": "fotovoltaic"
}

open_inscriptions: true if there are open inscriptions, false if not, null if this attribute can be ignored

inscriptions_url_form: URL of the form, "" if inscriptions are closed

implements OP#835