Introduce config to restrict user capabilities

crates/handlers/src/test_utils.rs

@@ -129,6 +129,9 @@ pub fn test_site_config() -> SiteConfig {
         imprint: None,
         password_login_enabled: true,
         password_registration_enabled: true,
+        email_change_allowed: true,
+        displayname_change_allowed: true,
+        password_change_allowed: true,
     }
 }