Network endpoint

Due to several open information, this commit implement an open data endpoint to retrieve open metrics in energy_communities.

This endpoint is: /api/opendata/network: retrieve the following open data information

{
    "energy_communities_active": 71,
    "energy_communities_goal": 1110,
    "energy_communities_total": 515,
    "inscriptions_in_activation": 444,
    "members": 2401
}