[IMP] energy_selfconsumption: integration invoicing

This is the Trello card

In this branch we worked on the last point of the requirements:

1. Changing the relationship between contract template and self-consumption so that contract template is linked to the product.
2. On the other hand, the obtaining of information is modified so that when the project is activated, contracts are created taking the values ​​stored in self-consumption.

energy_selfconsumption/models/product.py

@@ -11,3 +11,4 @@ class Product(models.Model):
         string="Energy Project",
         check_company=True,
     )
+    contract_template_id = fields.Many2one("contract.template")