refactor(watermark): use column instead of metadata on blob

db/migrate/20221222163907_add_watermarked_at_active_storage_blobs.rb

@@ -0,0 +1,5 @@
+class AddWatermarkedAtActiveStorageBlobs < ActiveRecord::Migration[6.1]
+  def change
+    add_column :active_storage_blobs, :watermarked_at, :datetime
+  end
+end

db/schema.rb

@@ -47,6 +47,7 @@ ActiveRecord::Schema.define(version: 2022_12_13_084442) do
     t.integer "lock_version"
     t.text "metadata"
     t.string "service_name", null: false
+    t.datetime "watermarked_at"
     t.index ["key"], name: "index_active_storage_blobs_on_key", unique: true
   end