docs: add diagrams visualizing "available date" and "visiblity date"

A PR that adds a diagram that visualizes how an update to a course run's availability date propogates through our systems.

cms/djangoapps/contentstore/docs/diagrams/visible_date_and_certificate_available_date.dsl

@@ -0,0 +1,48 @@
+/*
+ * This is a high level diagram visualizing how the `CERTIFICATE_AVAILBLE_DATE` and "visible date" attribute updates
+ * are updated internally and transmit to the Credentials IDA.
+ *
+ * It is written using Structurizr DSL (https://structurizr.org/).
+ */
+workspace {
+    model {
+        properties {
+            "structurizr.groupSeparator" "/"
+        }
+        author = person "Course Author" "External user from partner org with course authoring privileges in the CMS"
+        credentials = softwareSystem "Credentials IDA"
+        group "edx-platform" {
+            modulestore = element "edx-platform Mongo DB"
+            monolith_db = element "edx-platform Relational DB"
+            celery = softwareSystem "Celery"
+
+            group "CMS" {
+                studio = softwareSystem "CMS FrontEnd"
+                contentstore_app = softwareSystem "Contentstore Django app"
+            }
+            group "CORE (shared)" {
+                co_app = softwareSystem "CourseOverview Django App"
+                programs_app = softwareSystem "Programs Django App"
+            }
+        }
+
+        author -> studio "Updates certificate available date setting"
+        studio -> contentstore_app "Processes course settings update"
+        contentstore_app -> modulestore "Saves course settings update"
+        contentstore_app -> co_app "Emits COURSE PUBLISHED signal"
+        co_app -> modulestore "Retrieves course details from Mongo"
+        co_app -> monolith_db "Updates CourseOverview record"
+        co_app -> programs_app "Emits COURSE_CERT_DATE_CHANGED signal"
+        programs_app -> celery "Enqueue UPDATE_CERTIFICATE_VISIBLE_DATE task"
+        programs_app -> celery "Enqueue UPDATE_CERTIFICATE_AVAILABLE_DATE task"
+        celery -> credentials "REST requests to update `visible_date` attributes"
+        celery -> credentials "REST request to update `certificate_available_date` setting"
+    }
+
+    views {
+        systemLandscape "SystemLandscape" {
+            include *
+            autolayout lr
+        }
+    }
+}