Restrict flask version to <=2.2.3

[jwest115]

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Change Description

Restrict flask version to >=1.1.2 and <=2.2.3. Tested in python 3.9.6 virtual environment and was able to successfully install and start F´ GDS.

Rationale

From flask release notes:

Setting custom json_encoder and json_decoder classes on the app or a blueprint, and the corresponding json.JSONEncoder and JSONDecoder classes, are deprecated. JSON behavior can now be overridden using the app.json provider interface. pallets/flask#4692