Support items on subscriptions

[joannasese]

This PR adds support for items on subscriptions, where merchants may now associate a subscription add-on with an item in their catalog.

allow_any_item_on_subscriptions has been added to the Plan class. It is used to determine whether items can be assigned as add-ons to individual subscriptions. If true, items can be assigned as add-ons to individual subscription add-ons. If false, only plan add-ons can be used.

add_on_source, added to the SubscriptionAddOn class, is used to determine where the associated add-on data is pulled from. If this value is set to plan_add_on or left blank, then add-on data will be pulled from the plan's add-ons. If the associated plan has allow_any_item_on_subscriptions set to true and this field is set to item, then the associated add-on data will be pulled from the site's item catalog.

Code example:

// create sub add-on from item
$addon1 = new Recurly_SubscriptionAddOn();
$addon1->add_on_code = $item->item_code;
$addon1->add_on_source = "item";
$addon1->unit_amount_in_cents = 299;

// create sub add-on from existing add-on
$addon2 = new Recurly_SubscriptionAddOn();
$addon2->add_on_code = $add_on_2->add_on_code;

// create subscription
$subscription = new Recurly_Subscription();
$subscription->plan_code = $plan->plan_code;
$subscription->currency = 'USD';
$subscription->account = $account;
$subscription->subscription_add_ons = array($addon1, $addon2);
$subscription->create();

[bhelx]

👍

[bhelx]

👍