[CONF] Add ALLOWED_HOSTS in generated configuration

tools/conf/gargantext.template.ini

@@ -4,6 +4,8 @@
 DEBUG = {DEBUG}
 # SECURITY WARNING: keep the secret key used in production secret!
 SECRET_KEY = {SECRET_KEY}
+# Space-separated list of hosts
+ALLOWED_HOSTS =
 # PostgreSQL access
 DB_HOST = {DB_HOST}
 DB_PORT = {DB_PORT}