Backfill the significantly_updated_at from updated_at

We want to backfill the `significantly_updated_at` using the `updated_at`
attribute of each user.

db/migrate/20241122155145_backfill_significantly_updated_at.rb

@@ -0,0 +1,7 @@
+class BackfillSignificantlyUpdatedAt < ActiveRecord::Migration[7.1]
+  def up
+    User.in_batches do |batch|
+      batch.update_all("significantly_updated_at = updated_at")
+    end
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.1].define(version: 2024_11_20_082433) do
+ActiveRecord::Schema[7.1].define(version: 2024_11_22_155145) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "btree_gin"
   enable_extension "citext"