Option to have the appointable shortcode for a specific product and staff

[Valentina R]

Option to add the staff ID in the appointable product shortcode and then only display slots for that staff member (staff predefined).

Asked here: https://bookingwp.com/forums/topic/shortcode-to-display-appointment-of-a-single-shopstaff/

[Željan Topić]

Duplicate of #396.