Simple Font Awesome Icon plugin will give you the Font Awesome Icon option in your post and page. From there you can choose the required icon and hit save. Then use the get_post_meta(‘post ID’, ‘font-awesome-icon’, true); function in the template file and you will get the class name which can be used with i tag.
Please take a look the plugin page for more details: [https://codingdom.wordpress.com/simple-font-awesome-icon/)