✨ Re-export utils from Starlette (#1064)

* ✨ Re-export main features used from Starlette to simplify developer's code

* ♻️ Refactor Starlette exports

* ♻️ Refactor tutorial examples to use re-exported utils from Starlette

* 📝 Add examples for all middlewares

* 📝 Add new docs for middlewares

* 📝 Add examples for custom responses

* 📝 Extend docs for custom responses

* 📝 Update docs and add notes explaining re-exports from Starlette everywhere

* 🍱 Update screenshot for HTTP status

* 🔧 Update MkDocs config with new content

* ♻️ Refactor tests to use re-exported utils from Starlette

* ✨ Re-export WebSocketDisconnect from Starlette for tests

* ✅ Add extra tests for extra re-exported middleware

* ✅ Add tests for re-exported responses from Starlette

* ✨ Add docs about mounting WSGI apps

* ➕ Add Flask as a dependency to test WSGIMiddleware

* ✅ Test WSGIMiddleware example

docs/tutorial/response-status-code.md

@@ -64,9 +64,9 @@ Let's see the previous example again:
 
 But you don't have to memorize what each of these codes mean.
 
-You can use the convenience variables from `starlette.status`.
+You can use the convenience variables from `fastapi.status`.
 
-```Python hl_lines="2 7"
+```Python hl_lines="1 6"
 {!./src/response_status_code/tutorial002.py!}
 ```
 
@@ -74,6 +74,11 @@ They are just a convenience, they hold the same number, but that way you can use
 
 <img src="/img/tutorial/response-status-code/image02.png">
 
+!!! note "Technical Details"
+    You could also use `from starlette import status`.
+
+    **FastAPI** provides the same `starlette.status` as `fastapi.status` just as a convenience for you, the developer. But it comes directly from Starlette.
+
 ## Changing the default
 
 Later, in the **Advanced User Guide**, you will see how to return a different status code than the default you are declaring here.