On WooCommerce Subscriptions activation, reactivate any paused legacy subscriptions

[mattallan]

Project Thread: pgizk6-42-p2
Related Epic: #10401

This issue is being handled by the Chronos team as part of our Subscriptions Primary Offering project, as such, I've added this to our team's project board.

Note

This issue a follow-up to #10404

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• Targeted release: WooPayments 9.3

Description

There are a small number of US merchants using a legacy implementation of our Stripe Billing subscriptions feature without the WooCommerce Subscriptions extension. Back in 2023, we attempted to move merchants away from this, however that was not 100% successful.

This issue is part 4 of 5 where the goal is to upgrade these merchants from using deprecated Subscriptions code bundled in WooPayments (which is soon to be removed), to installing the WooCommerce Subscriptions extension to continue selling subscription products.

This issue comes one release before the woocommerce/subscriptions-core composer package is scheduled to be removed, as a follow-up to pausing any active legacy stripe billing subscriptions in #10404, if the merchant successfully installs WooCommerce Subscriptions extension, we want to reactivate any paused subscription so they continue to renew.

Acceptance Criteria

• Upon installing/activating WooCommerce Subscriptions, any legacy Stripe Billing subscriptions that were paused by Pause legacy Stripe Billing subscriptions on WooPayments 9.3 upgrade #10404 should automatically be reactivated/resume, assuming they're still within their current billing cycle.
• Implement some sort of cut-off period so that if these subscriptions are paused for 6 months, they don't reactivate and start charging the customer again. My thinking is we use the next renewal as the cut-off period.

Open questions

• This complicates things a little but should customers see their subscription as on-hold? If the subscription is going to be reactivated automatically, the customer probably shouldn't see it as on-hold, because then they can still decide to cancel/suspend it themselves, which will then prevent it from being reactivated automatically.