add middleware and postMessage

packages/slack/src/utils/required-scopes.ts

@@ -1 +1,3 @@
-export const requiredScopes: string[] = ['commands', 'team:read', 'chat:write', 'channels:history', 'groups:history', 'im:history', 'mpim:history'];
+export const requiredScopes: string[] = [
+  'commands', 'team:read', 'chat:write', 'channels:history', 'groups:history', 'im:history', 'mpim:history', 'app_mentions:read',
+];