📝 Add documentation about settings and env vars (#1118)

* Add doc and example for env var config

* Syntax highlight for .env file

* Add test for configuration docs

* 📝 Update settings docs, add more examples

* ✅ Add tests for settings

* 🚚 Rename "Application Configuration" to "Metadata and Docs URLs"

to disambiguate between that and settings

* 🔥 Remove replaced example file

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

tests/test_tutorial/test_metadata/test_tutorial001.py

@@ -1,6 +1,6 @@
 from fastapi.testclient import TestClient
 
-from application_configuration.tutorial001 import app
+from metadata.tutorial001 import app
 
 client = TestClient(app)
 

tests/test_tutorial/test_settings/test_app02.py

@@ -0,0 +1,9 @@
+from fastapi.testclient import TestClient
+
+from settings.app02 import main, test_main
+
+client = TestClient(main.app)
+
+
+def test_setting_override():
+    test_main.test_app()