Use SUPERSET_CONFIG_PATH env var to manage config

[kaapstorm]

This change uses the SUPERSET_CONFIG_PATH environment variable to manage Superset configuration, both for tests and for normal operation.

Calling hq_superset.patch_superset_config(superset_config) is unnecessary. The same can be achieved by including

FLASK_APP_MUTATOR = flask_app_mutator
CUSTOM_SECURITY_MANAGER = oauth.CommCareSecurityManager

in the config file.

I've added a comment to the start of superset_config.example.py to explain how to set the environment variable for normal operation. The environment variable is set automatically in hq_superset/tests/base_test.py for running tests.

[SmittieC]

@kaapstorm When I upgrade typing extensions locally, it works, but the version is larger than that which superset wants, so maybe we should merge this branch and see what it does with the later supset version?

[kaapstorm]

When I upgrade typing extensions ... see what it does with the later supset version?

I've rebased off master, which should resolve this. I'm watching the tests.

[kaapstorm]

Following up failures.

[kaapstorm]

Failures were caused by config_for_tests.py diverging from GitHub workflow config.