Currently if slides officers or managers define documentation courses as on payment there is no easy way for customers to buy it. In this commit we add a button on the frontend to allow the end user to buy a documentation course like a training course. This button is displayed only for on payment documentation courses, leaving other documentation courses displayed untouched. Task ID : 2125086 PR : odoo/odoo#40679 Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>