commerce_recurring 8.x-1.0-beta2

Changes since 8.x-1.0-beta1:

• #2932130 by bojanz: The subscription "ends" field should not use a 0 to indicate that it's empty
• #2924297 by bojanz, joachim, rszrama: Allow fixed billing periods to start on a specific day/month
• #2929899 by bojanz, joachim: Document why hard declines still result in retries
• #2928239 by bojanz: document in prorateOrderItem() how to differentiate between an initial order and a recurring order
• #2930824 by vasike: testBillingScheduleEditing fails
• #2929196 by joachim, bojanz: missing @group in SubscriptionLifecycleTest
• #2928984 by bojanz: Update for Commerce 2.2
• #2929784 by Almare, bojanz: OrderSubscriber needs to ignore recurring orders