feat: add E2E testing workflow for free version and update CI triggers

[ShahrearMSf]

### E2E Docker based Automation Workflow

It can now run e2e tests before every release. This suite approaches the plugin as a client would — it clicks through the UI, fills forms, navigates pages, and checks that things appear where they should. If something is broken, it will catch it before we ship. What it does:

1. Spins up a fresh WordPress + WooCommerce + NotificationX environment from scratch ✅
2. Walks through the plugin like a real user — creating notifications, verifying frontend display, checking analytics, testing navigation, and cleanup ✅
3. Tests CRUD operations — create, verify, delete (single + bulk) ✅
4. Covers few free notification types (WooCommerce, Comments, Cookie Notice, Notification Bar) via both Add New wizard and Quick Builder) ✅
5. Validates PRO limitations (popup checks for PRO-only types) ✅