🔧(mail) use new scaleway email gateway

We modify multiples things :
* settings.py in order to manage the new way to send email with the
scaleway gateway
* helm template to manage new mandatory secret
* helm configuration for staging/preprod/production

src/backend/people/settings.py

@@ -265,10 +265,12 @@ class Base(Configuration):
     # Mail
     EMAIL_BACKEND = values.Value("django.core.mail.backends.smtp.EmailBackend")
     EMAIL_HOST = values.Value(None)
+    EMAIL_HOST_USER = values.Value(None)
+    EMAIL_HOST_PASSWORD = values.Value(None)
     EMAIL_PORT = values.PositiveIntegerValue(None)
+    EMAIL_USE_TLS = values.BooleanValue(False)
     EMAIL_USE_SSL = values.BooleanValue(False)
     EMAIL_FROM = values.Value("from@example.com")
-
     AUTH_USER_MODEL = "core.User"
     INVITATION_VALIDITY_DURATION = 604800  # 7 days, in seconds