WooCommerce Subscriptions 6.9.0

* Fix: Cache the retry data needs migration logic to avoid a get_posts() call on every request. PR#2994
* Fix: Load the retry store instance on WordPress init rather than on Subscriptions plugin load. Fixes errors with third-party plugins hooking into get post queries and calling undeclared WP functions. PR#3000
* Fix: Fix an undefined product ID error which could occur during a switch request when trying to access a product from the old subscription format. PR#2961
* Fix: Fix a missing closing `a` tag in the downgrade notice. PR#3002
* Dev: Add a new hook ('woocommerce_admin_created_subscription') which is triggered after a subscription is created manually via the admin screen. PR#2988
* Dev: Add new hooks to allow third-parties to customize subscription filtering behavior on the admin subscriptions table. PR#2989

* New: Update Action Scheduler to v2.1.0.
* Fix: Remove the URL scheme when generating the site's duplicate lock URL. Fixes an issue where staging sites with a URL length equal the scheme would incorrectly not trigger staging mode. PR#2599
* Fix: Move callbacks attached specifically for renewal carts to the constructor so that all extended cart classes are not hooked on. PR#2963
* Fix: Allow products which are password protected to be manually renewed via the cart. PR#2912
* Fix: Remove unnecessary leading space in translation string. PR#2976
* Fix: Add group by clause to subscriber count reports query. PR#2970
* Fix: Fix an error which would occur when calling the deprecated get_related_orders_query(). PR#2954
* Tweak: Separate a subscription start from the creation date. PR#2594
* Tweak: Display the expected site URL in staging site notice and system status. PR#2950
* Dev: Implement an Autoloader for loading plugin class files. PR#2412
* Dev: Replace WC_Logger type hinting in function signatures to use lower level WC_Logger_Interface. PR#2902
* Dev: Remove switch_line_items_pre_2_1_2() and switch_shipping_line_items_pre_2_1_2() functions. PR#2900
* Dev: [WC 3.5] Move subscription customer ID's into the post author column on sites running WC 3.5 and above. PR#2559
* Dev: Move payment retry data to custom tables. PR#2753
* Dev: Update file inclusions to use relative paths. PR#2936
* Dev: Add an API for third-parties to register their custom subscription date types. PR#2840
* Dev: Update the hook used for adding Subscriptions Settings. PR#2939
* Dev: Add a 'wcs_payment_gateways_change_payment_method' filter to allow third-parties to filter which payment methods are displayed when changing payment methods. PR#2571
* Dev: Trigger a new 'wcs_before_replace_pay_shortcode' action before displaying the change payment shortcode.
* Dev: Add the 'wcs_update_all_subscriptions_addresses_checked' filter to allow third-parties to filter the default checked status of the all_subscriptions_addresses field. PR#2948

* Fix: Don't apply subscription payment gateway filters while on the order-pay page. PR#2927
* Fix: Prevent admin users from changing product type when the product has active subscriptions. PR#2932
* Fix: Avoid calculating the initial order carts shipping without an address. PR#2923
* Fix: Remove unnecessary empty() check for PHP < 5.5 compat. PR#2940
* Fix: Reinstate switch orders being returned from WC_Subscription::get_related_orders() when called with the default $order_type param. This returns the behavior of this function to what it was pre v2.3. PR#2946
* Tweak: [WC 3.4] Dont escape the product attribute labels in the add-to-cart/variable-subscription.php template. PR#2914
* Tweak: Add a link to the subscription customer's profile on the admin edit subscription screen. PR#2911
* Tweak: [dev] Update calls of remove_action() and remove_filter() removing the unused 4th parameter. PR#2926