✨ Add support for tag metadata in OpenAPI (#1348)

✨ Add support for tag metadata in OpenAPI (#1348)

* Allow to add OpenAPI tag descriptions

* fix type hint

* fix type hint 2

* refactor test to assure 100% coverage

* 📝 Update tags metadata example

* 📝 Update docs for tags metadata

* ✅ Move tags metadata test to tutorial subdir

* 🎨 Update format in applications

* 🍱 Update docs UI image based on new example

* 🎨 Apply formatting after solving conflicts

Co-authored-by: Sebastián Ramírez <tiangolo@gmail.com>