Subscribe block: Improve next step after "Confirm your subscription"

### Impacted plugin

Jetpack

### What


In the email `Confirm your subscription`, upon clicking `Confirm email`, could we _redirect to a page acknowledging the subscription, stating that an email was sent – not to the WordPress.com account._

User request: https://wordpress.org/support/topic/subscription-widget-not-working-6/#post-17360704

### How

I tested it, `Confirm email` auto-logins when applicable, and goes to https://wordpress.com/sites, but a better page might be https://wordpress.com/read/subscriptions/pending with a message to `Confirm` the subscription.

Start by tracing the Confirm email link from the “Confirm your subscription” email through the Jetpack subscription flow, then inspect the current redirect to wordpress.com/sites and the proposed /read/subscriptions/pending destination. Done means the user reaches an acknowledgement page explaining that a subscription-confirmation email was sent, rather than being sent to the WordPress.com account.

Written by the indexing model from the issue text.