type annotations would improve Example docs and reduce confusion

I suggest adding type-annotations to these examples to clarify what's happening

[We have this example:
](https://flask-smorest.readthedocs.io/en/latest/quickstart.html)@blp.arguments(PetSchema)
@blp.response(201, PetSchema)
def post(self, new_data):
"""Add a new pet"""
item = Pet.create(**new_data)
return item

If "PetSchema" know's how to encode and decode it's respective model/dataclass, then I would expect "new_data" to be a PetModel ... but this code makes it clear that it's only a dictionary

Type annotations would clear this up for newbies and I'd also like clear examples that show how to make PetSchema smart enough to pass a dataclass (object with useful methods) into the handler

Start with the Quickstart example linked in the issue and inspect how its PetSchema and handler are documented. Clarify the type of new_data with annotations and add an example showing how PetSchema can pass a dataclass to the handler; done means the examples accurately explain dictionary versus model-like data for newcomers.

Written by the indexing model from the issue text.