feat: add backend_url config option

Required for refresh_token cookie to work properly

src/api/v1/auth/register.rs

@@ -146,7 +146,7 @@ pub async fn res(
             .await?;
 
         return Ok(HttpResponse::Ok()
-            .cookie(new_refresh_token_cookie(refresh_token))
+            .cookie(new_refresh_token_cookie(&data.config, refresh_token))
             .json(Response { access_token }));
     }