How do I make a Page Template available to my Custom Post Types?

From WordPress version 4.7 you can now assign custom page templates to other post types along with page.

To achieve this in addition to the Template Name file header, the post types supported by a template can be specified using Template Post Type: as following.

<?php
/*
Template Name: Full-width page layout
Template Post Type: post, page, product
*/

More Information:
https://make.wordpress.org/core/2016/11/03/post-type-templates-in-4-7/