reverting json setting to use json_encoder despite warnings

[gfeldman]

closes: 26527

The flask_app.json_provider_class does not take a JsonEncoder as an argument. Reverting the setting to flask_app.json_encoder despite deprecation warnings until a provider can be written.

[boring-cyborg]

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[gfeldman]

with flask_app.json_encoder = AirflowJsonEncoder setting

>>> from airflow.www import app
>>> from kubernetes.client import models as k8s
>>> p = k8s.V1Pod(spec=k8s.V1PodSpec(containers=[k8s.V1Container(name="base")]))
>>> c = app.create_app()
>>> c.json.dumps(p)
'{"spec": {"containers": [{"name": "base"}]}}'

with flask_app.json_provider_class = AirflowJsonEncoder

>>> from airflow.www import app
>>> from kubernetes.client import models as k8s
>>> p = k8s.V1Pod(spec=k8s.V1PodSpec(containers=[k8s.V1Container(name="base")]))
>>> c = app.create_app()
>>> c.json.dumps(p)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/guy.feldman/opt/anaconda3/lib/python3.9/site-packages/flask/json/provider.py", line 230, in dumps
    return json.dumps(obj, **kwargs)
  File "/Users/guy.feldman/opt/anaconda3/lib/python3.9/json/__init__.py", line 234, in dumps
    return cls(
  File "/Users/guy.feldman/opt/anaconda3/lib/python3.9/json/encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "/Users/guy.feldman/opt/anaconda3/lib/python3.9/json/encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "/Users/guy.feldman/opt/anaconda3/lib/python3.9/site-packages/flask/json/provider.py", line 122, in _default
    raise TypeError(f"Object of type {type(o).__name__} is not JSON serializable")
TypeError: Object of type V1Pod is not JSON serializable

[ashb]

This fix is incorrect, json_encoder is now deprecated in Flask 2.2 and will be removed in flask 2.3
https://flask.palletsprojects.com/en/2.2.x/api/?highlight=json_provider_class#flask.Flask.json_encoder

So we'll need to find a different fix.

[ashb]

Closing in favour of #26554. Thank you for the debugging steps, they made it very easy for me to fix.