Improvement: cloud functions to add user from @montpellier-techhub.org to admins #48

When a new user register using it's montpellier-techhub.org, we should add him to admins.

TODO: this involve changing the deploy script as we'll need to deploy some serverless stuff at the same time

• Trigger a cloud function on user creating + update 'permissions' with the user if email valid. Help here
• figure out the deploy we need to do.