For authenticated users that are not global staff, changing discussion
providers after a course has started fails with 403 Forbidden.
Related issues:
* [BB-4253](https://tasks.opencraft.com/browse/BB-4253)
* [TNL-8142](https://openedx.atlassian.net/browse/TNL-8142)
BREAKING CHANGE:
Course staff, who were previously allowed to do this operation,
will instead receive a 403 Forbidden response.
Code in ./common/lib/xmodule/xmodule should
be imported as `from xmodule`, since `xmodule`
is a locally-installed package.
This is weird, but as long as it is the case,
we should be consistent.
(In BOM-2584, I propose moving the files to
./xmodule, which would quell this confusion.)
This commit adjusts a few values in our discussions configuration APIs to make them match what the frontend needs, as well as to more accurately reflect the providers available today.
- The `active` provider ID is expressed as None if it doesn’t exist
- The “cs_comments_service” provider has been renamed “legacy” - when we implement the new discussions micro-frontend, we’ll also have a separate provider for that, so they can’t both be “cs_comments_service”. Also, cs_comments_service is such a bad name for anything.
- The hard-coded providers list in get_supported_providers now includes ‘legacy’ and ‘piazza’, our two known providers. This list will be updated as more known providers come online.
- The PROVIDER_FEATURE_MAP has similarly been updated.
Part of this task: TNL-8093
