Connexion: Use orjson instead of json for JSON serialization

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Description

The authors of orjson describe it like this:

orjson is a fast, correct JSON library for Python. It benchmarks as the fastest Python library for JSON and is more correct than the standard json library or other third-party libraries.

Based on the benchmarks the authors have shared, orjson is 5 to 50 times faster than the standard json library.

Expected behaviour

Add an option to use orjson instead of json.

Actual behaviour

json is the only option for JSON serialization.

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Comparing the standard Jsonifier used by Connexion and orjson in an example API call in my application, I see the difference in performance can be extreme, 570 times faster:

FlaskApi._serialize_data():

# 2434078 bytes, total time 8ms
body = orjson.dumps(data, option=orjson.OPT_NAIVE_UTC | orjson.OPT_NON_STR_KEYS)

# 3899087 bytes, total time 4565ms
body = cls.jsonifier.dumps(data)

To validate the output, I used json.loads() and verified that it creates identical objects. It does.