Describe the bug
Can't validate a response whose pydantic validation model contains a date.

To Reproduce

• Add a model with a date:

class HistoryDate(BaseModel):
    date: date

• use it in a GET route

import datetime
@app.route("/api/date_naive_not_working", methods=["GET"])
@api.validate(resp=Response(HTTP_200=HistoryDate))
def not_working_date_naive():
    historyDate = HistoryDate(date=datetime.date.today())
    # will throw not serializable cause flask default encoders are used
    return jsonify(historyDate)

• use the route => 500

resp = client.get(
        "/api/date_naive_not_working"
    )
assert resp.status_code == 500

Expected behavior
The response is valid and should be validated.

Error Message
The pydantic model is not JSON serializable

Desktop (please complete the following information):

• OS: Linux
• Version Mint, docker debian

Python Information (please complete the following information):

• Python Version 3.10.1
• Library Version 0.2.1
• Other dependencies 2.0.2

Additional context

I am quite new in the pydantic world. Very pleased so far and thank you for this great addition which completely meets my need.

I turned around this as I had the impression to take the lib the wrong way.
Turns out the only workaround, I found is:

@app.route("/api/date_cumbersome", methods=["GET"])
@api.validate(resp=Response(HTTP_200=HistoryDate))
def working_date_validation_cumbersome():
    historyDate = HistoryDate(date=API_DATE_TODAY)
    return jsonify(json.loads(historyDate.json()))

It's actually a pydantic issue in some ways.
There is no other ways (yet) to get a json ready dict (pydantic/pydantic#951 (comment)) to feed the Flask serializer with.

Nevertheless to stumble upon this is quite confusing and frustrating.
I propose a way that does not change anything to this lib but avoid this frustration: allow to pass by flask jsonify method to use pydantic json method instead. I am not very happy with this but let's consider it as a starter for discussion.

I am submitting a PR to expose the problem and my modest proposition.
The PR will have tests which will expose the issue and the workaround of serializing/deserializing.