* Add - When a customer toggles automatic renewals on or off via their My Account page, add a note to the subscription to record that event.
* Fix - When a subscription is flagged as requiring manual payments, allow admin users to turn on automatic payments for a subscription via the Edit Subscription page by selecting a new payment method.
* Fix - When processing an early renewal order, make sure the suspension count is reset back to 0 on payment complete.
* Fix - Ensure proper backfilling of subscription metadata (i.e. dates and cache) to the postmeta table when HPOS is enabled and compatibility mode (data syncing) is turned on.
* Fix - Fetch and update the `_cancelled_email_sent` meta in a HPOS compatibile way.
* Dev - Introduce a new wcs_get_subscription_grouping_key() function to generate a unique key for a subscription based on its billing schedule. This function uses the existing recurring cart key concept.
* Dev - Deprecate the WC_Subscriptions_Synchroniser::add_to_recurring_cart_key(). Use WC_Subscriptions_Synchroniser::add_to_recurring_product_grouping_key() instead.
