DEV: Add timestamp columns to optimized_images table (#10199)

This allows us to filter by created/updated date when comparing to an S3 inventory.

db/migrate/20200709094846_add_timestamps_to_optimized_images.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+class AddTimestampsToOptimizedImages < ActiveRecord::Migration[6.0]
+  def change
+    add_column :optimized_images, :created_at, :datetime, null: true
+    add_column :optimized_images, :updated_at, :datetime, null: true
+
+    # Start by stealing created/updated at from the uploads table
+    # Not perfect, but a good approximation
+    execute <<~SQL
+      UPDATE optimized_images
+      SET created_at = uploads.created_at,
+          updated_at = uploads.created_at
+      FROM uploads
+      WHERE uploads.id = optimized_images.upload_id
+    SQL
+
+    # Integrity is not enforced, we might have optimized images
+    # with no uploads
+    execute <<~SQL
+      UPDATE optimized_images
+      SET created_at = NOW(),
+          updated_at = NOW()
+      WHERE created_at IS NULL
+    SQL
+
+    execute <<~SQL
+      ALTER TABLE optimized_images ALTER COLUMN created_at SET NOT NULL;
+    SQL
+
+    execute <<~SQL
+      ALTER TABLE optimized_images ALTER COLUMN updated_at SET NOT NULL;
+    SQL
+  end
+end