dev: add function-flag feature flag type

src/backend/src/services/FeatureFlagService.js

@@ -42,10 +42,21 @@ class FeatureFlagService extends BaseService {
         if ( ! this.known_flags.has(permission) ) {
             this.known_flags.set(permission, true);
         }
-        
+
+        if ( this.known_flags[permission].$ === 'config-flag' ) {
+            return this.known_flags[permission].value;
+        }
 
         const actor = options.actor ?? Context.get('actor');
 
+        if ( this.known_flags[permission].$ === 'function-flag' ) {
+            return await this.known_flags[permission].fn({
+                ...options,
+                actor
+            });
+        }
+        
+
         const svc_permission = this.services.get('permission');
         const reading = await svc_permission.scan(actor, `feature:${permission}`);
         const l = PermissionUtil.reading_to_options(reading);
@@ -60,6 +71,10 @@ class FeatureFlagService extends BaseService {
                 summary[key] = value.value;
                 continue;
             }
+            if ( value.$ === 'function-flag' ) {
+                summary[key] = await value.fn({ actor });
+                continue;
+            }
             const svc_permission = this.services.get('permission');
             const reading = await svc_permission.scan(actor, `feature:${key}`);
             const l = PermissionUtil.reading_to_options(reading);