Show discounted amount in the cost section (used with WC Memberships)

[Valentina R]

As explained here: https://bizzthemes.com/forums/topic/need-to-display-the-discount-amount-in-calendar-using-wc-membership-plugin/

[Željan Topić]

This won't be added to core and customers can add the modification by hooking into the "woocommerce_appointments_appointment_cost_html" filter and modifying the cost HTML output.