Set member status to sustainer upon payment

Introduces a state machine for the payment status as well.

refs #213

db/migrate/20250527113805_update_payment_status_to_pending.rb

@@ -0,0 +1,6 @@
+class UpdatePaymentStatusToPending < ActiveRecord::Migration[8.0]
+  def change
+    Donation.where(payment_status: nil).update_all(payment_status: "pending")
+    Donation.where.not(payment_status: %w[pending processing settled]).update_all(payment_status: "pending")
+  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[8.0].define(version: 2025_05_17_105755) do
+ActiveRecord::Schema[8.0].define(version: 2025_05_27_113805) do
   create_table "active_storage_attachments", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false