Modify the Filtering docs to include an import for Query and mention serialization

[swills1]

This is in regard to https://django-ninja.dev/guides/input/filtering/.

I feel like the very first example should import Query to support the example directly under it and to create the underlying understanding for that doc page as you read.

from ninja import FilterSchema, Field, Query
from typing import Optional


class BookFilterSchema(FilterSchema):
    name: Optional[str] = None
    author: Optional[str] = None
    created_after: Optional[datetime] = None

I think you may mention serialization or link to a central doc page talking about the need for it. (Other docs page examples show the serialization.) When I followed the examples as is, I got a json serialization error. When I serialized it, the problem was fixed and my responses came back perfectly.

Also, this was sort of intuitive, but I did have to read the example twice to catch it. You may mention the = None is what makes a field required or not. Just a small note or even comment next to one of the lines.

from ninja import NinjaAPI, Query, Schema
from api.models import People
from django.http import JsonResponse


class PeopleFilterSchema(Schema):
    id: int | None = None
    first_name: str | None = None
    last_name: str | None = None


@api.get("/people")
def list_people(request, filters: PeopleFilterSchema = Query(None)):
    queryset = People.objects.all()
    if filters.id:
        queryset = queryset.filter(id=filters.id)
    if filters.first_name:
        queryset = queryset.filter(first_name=filters.first_name)
    if filters.last_name:
        queryset = queryset.filter(last_name=filters.last_name)
    
    # Serialize queryset to JSON
    serialized_data = list(queryset.values("id", "first_name", "last_name"))
    return JsonResponse(serialized_data, safe=False)