SUPERSET_PROXY_FIX enhancements

[bmtcril]

Currently we're supporting Superset / Flask's proxy fix setting:

• tutor-contrib-aspects/tutoraspects/plugin.py

  Line 368 in 40bbb1a

  ("SUPERSET_ENABLE_PROXY_FIX", "{{ENABLE_WEB_PROXY}}"),

• https://flask.palletsprojects.com/en/latest/deploying/proxy_fix/
• https://github.com/apache/superset/blob/09e9c6a522ecf3cebb618fec3a965d2b55f298ad/superset/config.py#L331

However we're not exposing the fine grained config for it:

• https://github.com/apache/superset/blob/09e9c6a522ecf3cebb618fec3a965d2b55f298ad/superset/config.py#L332

The need for the proxy fix has come up a few times, so it's just a matter of time before we need the other controls, we should get ahead of that as time permits. Should just be a matter of either adding the dict or the 5 settings in it to tutor-contrib-aspects and passing in to the Superset config.