Make the checkbox on the change payment method page which updates all subscriptions enabled by default

[mattallan]

Supersedes https://github.com/Automattic/woocommerce-subscriptions-core/pull/586 Fixes 4372-gh-woocommerce/woocommerce-subscriptions Slack p1710775338910969-slack-C7U3Y3VMY

Description

According to the linked issue, merchants are regularly contacting support confused as to why their customers are updating their payment details but their other subscriptions were not updating, and as reported in the issue, this is mostly due to the checkbox option being missed by customers:

This isn't a good merchant or customer experience so in the slack thread, I proposed the idea of simply changing this checkbox to be enabled by default which I've done in this PR:

Some other changes I've made:

• Make the field required. This is to remove the "(optional)" text which didn't make much sense if the field was enabled by default. But also puts a red * next to the field to make it a bit more noticeable by customers
• Change the text of the field slightly.

How to test this PR

1. Have a payment method that supports changing payment methods (i.e. Stripe)
2. Have multiple subscriptions purchased to prompt the update all my subscriptions flow
3. Visit My Account > Subscriptions > View Subscription
4. Click on Change payment action
5. Notice the field is selected by default on page load

Product impact

• [x] Added changelog entry (or does not apply)
• [ ] Will this PR affect WooCommerce Subscriptions? yes/no/tbc, add issue ref
• [ ] Will this PR affect WooCommerce Payments? yes/no/tbc, add issue ref
• [ ] Added deprecated functions, hooks or classes to the spreadsheet