docs: add decision record for master branch split

docs/decisions/0008-master-branch-split.rst

@@ -0,0 +1,52 @@
+8. Master branch split from 2u/main
+------------------------------------------------------------
+
+Status
+------
+
+Accepted
+
+Context
+-------
+
+Both 2U and Openedx use ecommerce's master branch for releases. Occasionally, changes
+specific to 2U's business case are merged into code, which also influences the structure
+of the code that the community runs, even if the changes are not relevant or beneficial
+to the community at large.
+
+Additionally, 2U has internal compliance checks that can slow the release cycle of
+major changes to ecommerce (e.g. django 4.2). This puts Openedx at risk of releasing
+with deprecated packages.
+
+Decision
+--------
+
+A new protected branch will be created named "2u/main", which 2U will continue to use
+as its own main branch, while leaving "master" branch to the community.
+
+Consequences
+------------
+
+This allows the community to move forward with contributions on "master" without risk of
+breaking functionality for 2U or 2U committing changes to "master" that are irrelevant or
+otherwise inappropriate for the community's use case.
+
+Because protected branches in ecommerce require a user with Write access to the repository,
+the "master" branch will now require someone from the community to review and manage
+code contributions to that branch.
+
+Rejected Alternatives
+---------------------
+
+Repo fork
+~~~~~~~~~
+
+Why not fork the repo entirely? 2U and the community use a shared set of tools for
+working in development environments. While working from separate branches and repo
+forks are functionally equivalent, working in separate branches allows for
+minimal updates to shared tooling to support this change. One can simply checkout a
+branch name, without needing the tooling to be updated to know about non Openedx
+git remotes.
+
+This is not a one way door, and if we decide later the a proper repo fork is a better
+solution, then we are open to making adjustments.