✨ 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/query_params_str_validations/tutorial004.py

@@ -1,4 +1,4 @@
-from typing import Optional
+from typing import Union
 
 from fastapi import FastAPI, Query
 
@@ -7,7 +7,9 @@ app = FastAPI()
 
 @app.get("/items/")
 async def read_items(
-    q: Optional[str] = Query(None, min_length=3, max_length=50, regex="^fixedquery$")
+    q: Union[str, None] = Query(
+        default=None, min_length=3, max_length=50, regex="^fixedquery$"
+    )
 ):
     results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
     if q: