Add record to track overridden limits

Before, we were relying on just changing the cards_count in account, but this
could create problems where the system to calculate the next card number fails due
to the unique constraint.

saas/test/controllers/admin/overridden_limits_controller_test.rb

@@ -0,0 +1,22 @@
+require "test_helper"
+
+class Admin::OverriddenLimitsControllerTest < ActionDispatch::IntegrationTest
+  test "staff can reset overridden limits" do
+    sign_in_as :david
+    account = accounts(:"37s")
+
+    # First set an override
+    account.override_limits(card_count: 500)
+    assert_equal 500, account.reload.billed_cards_count
+
+    # Then reset it
+    untenanted do
+      delete saas.admin_account_overridden_limits_path(account.external_account_id)
+      assert_redirected_to saas.edit_admin_account_path(account.external_account_id)
+    end
+
+    # Verify override was removed
+    assert_nil account.reload.overridden_limits
+    assert_equal account.cards_count, account.billed_cards_count
+  end
+end