Review Python Requirements

[AlexCatarino]

We build Lean CLI for Python versions 3.7 to 3.10
https://github.com/QuantConnect/lean-cli/blob/master/.github/workflows/build.yml#L12
However, quantconnect-stubs depends on pandas>=1.5.3, and pandas 1.5 doesn't support Python 3.8.
https://pandas.pydata.org/pandas-docs/version/1.5/getting_started/install.html

Users with Python 3.7 can't install recent versions of Lean CLI:

ERROR: Cannot install lean because these package versions have conflicting dependencies.

The conflict is caused by:
quantconnect-stubs 16243 depends on pandas>=1.5.3

[Martin-Molinero]

quantconnect-stubs will no longer enforce a pandas or matplotlib version, see QuantConnect/quantconnect-stubs-generator#18