* feat: update preview url to direct to mfe
* fix: use url builder instead of string formatter
* fix: url redirect for never published units
* fix: remove 404 error when not a preview or staff
* feat: update sequence metadata to allow draft branch
This introdues the idea of "upstream" and "downstream" content,
where downstreams (like course components) can pull content updates from
upstreams (like learning core-backed content library blocks). This
supports the upcoming Content Libraries Relaunch Beta for Sumac.
New features include:
* A new XBlockMixin: UpstreamSyncMixin.
* A new CMS Python API: cms.lib.xblock.upstream_sync
* A new CMS JSON API: /api/contentstore/v2/downstreams
* A temporary, very basic UI for syncing from Content Library blocks
Implements:
https://github.com/kdmccormick/edx-platform/blob/kdmccormick/upstream-proto/docs/decisions/0020-upstream-block.rst
Co-authored-by: Braden MacDonald <braden@opencraft.com>
