✨ Add support for not needing ... as default value in required Query(), Path(), Header(), etc. (#4906)

* ✨ Do not require default value in Query(), Path(), Header(), etc

* 📝 Update source examples for docs with default and required values

* ✅ Update tests with new default values and not required Ellipsis

* 📝 Update docs for Query params and update info about default value, required, Ellipsis

docs_src/request_forms/tutorial001.py

@@ -4,5 +4,5 @@ app = FastAPI()
 
 
 @app.post("/login/")
-async def login(username: str = Form(...), password: str = Form(...)):
+async def login(username: str = Form(), password: str = Form()):
     return {"username": username}