Add root_account_id to conversation_participants

Closes PLAT-5603
flag=none

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

Change-Id: I396cd193512cae37976241c73ff6e595b4e6083c
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/235265
Tested-by: Service Cloud Jenkins <[email protected]>
QA-Review: Weston Dransfield <[email protected]>
Product-Review: Weston Dransfield <[email protected]>
Reviewed-by: Rob Orton <[email protected]>

db/migrate/20200424201444_add_root_account_id_to_conversation_participants.rb

@@ -0,0 +1,32 @@
+#
+# Copyright (C) 2020 - present Instructure, Inc.
+#
+# This file is part of Canvas.
+#
+# Canvas is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Affero General Public License as published by the Free
+# Software Foundation, version 3 of the License.
+#
+# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
+# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along
+# with this program. If not, see <http://www.gnu.org/licenses/>.
+
+class AddRootAccountIdToConversationParticipants < ActiveRecord::Migration[5.2]
+  include MigrationHelpers::AddColumnAndFk
+
+  tag :predeploy
+  disable_ddl_transaction!
+
+    def up
+    add_column_and_fk :conversation_participants, :root_account_id, :accounts
+    add_index :conversation_participants, :root_account_id, algorithm: :concurrently
+  end
+
+  def down
+    remove_column :conversation_participants, :root_account_id
+  end
+end