✨ 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>

docs_src/metadata/tutorial004.py

@@ -0,0 +1,28 @@
+from fastapi import FastAPI
+
+tags_metadata = [
+    {
+        "name": "users",
+        "description": "Operations with users. The **login** logic is also here.",
+    },
+    {
+        "name": "items",
+        "description": "Manage items. So _fancy_ they have their own docs.",
+        "externalDocs": {
+            "description": "Items external docs",
+            "url": "https://fastapi.tiangolo.com/",
+        },
+    },
+]
+
+app = FastAPI(openapi_tags=tags_metadata)
+
+
+@app.get("/users/", tags=["users"])
+async def get_users():
+    return [{"name": "Harry"}, {"name": "Ron"}]
+
+
+@app.get("/items/", tags=["items"])
+async def get_items():
+    return [{"name": "wand"}, {"name": "flying broom"}]