refactor: move coursegraph to cms

This code was originally located at:
  ./openedx/core/djangoapps/coursegraph

However, code makes more sense within the ./cms tree, because:
* it is responsible for publishing course content to an
  external system, with is within the responsibilities of CMS, and
* is uses modulestore, which is discouraged for use in LMS
  (see 0011-limit-modulestore-use-in-lms.rst).

So, we move the code to:
  ./cms/djangoapps/coursegraph
and uninstall coursegraph from LMS.

We do not expect this refactor to have any breaking downstream effects.

.github/workflows/unit-test-shards.json

@@ -99,7 +99,6 @@
       "openedx/core/djangoapps/course_apps/",
       "openedx/core/djangoapps/course_date_signals/",
       "openedx/core/djangoapps/course_groups/",
-      "openedx/core/djangoapps/coursegraph/",
       "openedx/core/djangoapps/courseware_api/",
       "openedx/core/djangoapps/crawlers/",
       "openedx/core/djangoapps/credentials/",
@@ -181,7 +180,6 @@
       "openedx/core/djangoapps/course_apps/",
       "openedx/core/djangoapps/course_date_signals/",
       "openedx/core/djangoapps/course_groups/",
-      "openedx/core/djangoapps/coursegraph/",
       "openedx/core/djangoapps/courseware_api/",
       "openedx/core/djangoapps/crawlers/",
       "openedx/core/djangoapps/credentials/",
@@ -240,6 +238,7 @@
     "paths": [
       "cms/djangoapps/api/",
       "cms/djangoapps/cms_user_tasks/",
+      "cms/djangoapps/coursegraph/",
       "cms/djangoapps/course_creators/",
       "cms/djangoapps/export_course_metadata/",
       "cms/djangoapps/maintenance/",