add sticker column to submissions table

closes EVAL-2976
flag=submission_stickers

Test Plan:
- run migrations
- open a rails console, and fetch a submission:

  s = Submission.first

- verify the submission has a default sticker of `nil`:

  s.sticker
  => nil

- verify the sticker can be updated:

  s.update!(sticker: "foo")

- verify the sticker name cannot exceed 255 characters

  s.update!(sticker: "a" * 255) # should succeed
  s.update!(sticker: "a" * 256) # should fail

Change-Id: I0839c5848438db5ad8fbf5bdb568187578c68afb
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/313762
Reviewed-by: Christopher Soto <christopher.soto@instructure.com>
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Migration-Review: Jacob Burroughs <jburroughs@instructure.com>
QA-Review: Spencer Olson <solson@instructure.com>
Product-Review: Cameron Ray <cameron.ray@instructure.com>

db/migrate/20230723200626_add_sticker_to_submissions.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+#
+# Copyright (C) 2023 - 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 AddStickerToSubmissions < ActiveRecord::Migration[7.0]
+  tag :predeploy
+
+  def change
+    add_column :submissions, :sticker, :string, limit: 255
+  end
+end