✨ 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/body_fields/tutorial001.py

@@ -1,4 +1,4 @@
-from typing import Optional
+from typing import Union
 
 from fastapi import Body, FastAPI
 from pydantic import BaseModel, Field
@@ -8,14 +8,14 @@ app = FastAPI()
 
 class Item(BaseModel):
     name: str
-    description: Optional[str] = Field(
-        None, title="The description of the item", max_length=300
+    description: Union[str, None] = Field(
+        default=None, title="The description of the item", max_length=300
     )
-    price: float = Field(..., gt=0, description="The price must be greater than zero")
-    tax: Optional[float] = None
+    price: float = Field(gt=0, description="The price must be greater than zero")
+    tax: Union[float, None] = None
 
 
 @app.put("/items/{item_id}")
-async def update_item(item_id: int, item: Item = Body(..., embed=True)):
+async def update_item(item_id: int, item: Item = Body(embed=True)):
     results = {"item_id": item_id, "item": item}
     return results