Refactor LTI parameters and add study group

* This change also requires that submissions in our test need to have a valid study group.

db/migrate/20230819084916_add_study_group_to_lti_parameters.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+class AddStudyGroupToLtiParameters < ActiveRecord::Migration[7.0]
+  def change
+    add_reference :lti_parameters, :study_group, index: true, null: true, foreign_key: true
+  end
+end