add submission tracking events

db/migrate/20230910084410_create_submission_events.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+class CreateSubmissionEvents < ActiveRecord::Migration[7.0]
+  def change
+    create_table :submission_events do |t|
+      t.references :submission, null: false, foreign_key: true, index: true
+      t.references :submitter, null: true, foreign_key: true, index: true
+      t.text :data, null: false
+      t.string :event_type, null: false
+      t.datetime :event_timestamp, null: false
+
+      t.timestamps
+    end
+  end
+end