Add root_account_id to content_participations

Closes PLAT-5562
flag=none

Test Plan:
- Verify migrations run
- Verify a root_account_id can be set on a
  ContentParticipation record
- Verify ContentParticipation always live on
  the same shard as their root account

Change-Id: Ia7e766c3633f0864ba1158e71e7d47b9573dc9cb
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/233680
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Weston Dransfield <wdransfield@instructure.com>
Product-Review: Weston Dransfield <wdransfield@instructure.com>

db/migrate/20200410155410_add_root_account_id_to_content_participations.rb

@@ -0,0 +1,27 @@
+#
+# Copyright (C) 2020 - present Instructure, Inc.
+#
+# This file is part of Canvas.
+#
+# Canvas is free software: you can redistribute it and/or modify
+# the terms of the GNU Affero General Public License as publishe
+# Software Foundation, version 3 of the License.
+#
+# Canvas is distributed in the hope that it will be useful, but 
+# WARRANTY; without even the implied warranty of MERCHANTABILITY
+# A PARTICULAR PURPOSE. See the GNU Affero General Public Licens
+# details.
+#
+# You should have received a copy of the GNU Affero General Publ
+# with this program. If not, see <http://www.gnu.org/licenses/>.
+
+class AddRootAccountIdToContentParticipations < ActiveRecord::Migration[5.2]
+  tag :predeploy
+  disable_ddl_transaction!
+
+  def change
+    add_column :content_participations, :root_account_id, :integer, limit: 8
+    add_foreign_key :content_participations, :accounts, column: :root_account_id
+    add_index :content_participations, :root_account_id, algorithm: :concurrently
+  end
+end