Add 'Learn More' link to PPE deprecation hub on settings page

When viewing PayPal Express gateway settings, show a 'Learn More'
button linking to the deprecation hub blog post.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: dparker1005

adminpages/paymentsettings.php

@@ -354,6 +354,9 @@
 						?>
 					</p>
 					<p>
+						<?php if ( 'paypalexpress' === $edit_gateway ) { ?>
+							<a class="button button-secondary" href="https://www.paidmembershipspro.com/paypal-express-deprecation-hub/?utm_source=plugin&utm_medium=pmpro-paymentsettings&utm_campaign=blog&utm_content=paypal-express-deprecation" target="_blank" rel="nofollow noopener"><?php esc_html_e('Learn More', 'paid-memberships-pro' ); ?></a>
+						<?php } ?>
 						<a class="button button-secondary" href="https://www.paidmembershipspro.com/documentation/compatibility/incompatible-deprecated-add-ons/?utm_source=plugin&utm_medium=pmpro-paymentsettings&utm_campaign=documentation&utm_content=deprecated-gateways#deprecated-payment-gateways" target="_blank" rel="nofollow noopener"><?php esc_html_e('About Deprecated Gateways', 'paid-memberships-pro' ); ?></a>
 						<a class="button" href="https://www.paidmembershipspro.com/switching-payment-gateways/?utm_source=plugin&utm_medium=pmpro-paymentsettings&utm_campaign=blog&utm_content=switching-payment-gateways" target="_blank" rel="nofollow noopener"><?php esc_html_e('How to Switch Payment Gateways', 'paid-memberships-pro' ); ?></a>
 					</p>