change auth companion attribute names

[Anas12091101]

What are the relevant tickets?

https://github.com/mitodl/hq/issues/4142

Description (What does it do?)

The mitxpro-openedx-extensions are being moved to the open-edx-plugins repository, where we are changing the name of the package to something more generic since the same package is also being used by mitxonline. For this, some setting attribute names have been changed in this PR, including the attribute MITXPRO_CORE_REDIRECT_ALLOW_RE_LIST. This PR changes the name MITXPRO_CORE_REDIRECT_ALLOW_RE_LIST to MITX_REDIRECT_ALLOW_RE_LIST.

Note: This PR should be merged after https://github.com/mitodl/open-edx-plugins/pull/328