Compatibility with flask 2.3.0

[viniciuschiele]

• Make flask-apscheduler compatible with flask 2.3.0
• Change minimum required flask version to 2.2.0
• Fix Flask 2.3.2 causing KeyError: 'JSONIFY_PRETTYPRINT_REGULAR' #226

[codecov]

Codecov Report

Patch coverage: 87.50% and project coverage change: +0.09 🎉

Comparison is base (d5775be) 91.55% compared to head (d0490ac) 91.64%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #227      +/-   ##
==========================================
+ Coverage   91.55%   91.64%   +0.09%     
==========================================
  Files           6        6              
  Lines         438      431       -7     
==========================================
- Hits          401      395       -6     
+ Misses         37       36       -1     

Impacted Files	Coverage Δ
flask_apscheduler/json.py	92.85% <87.50%> (+2.38%)	⬆️

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