@appngamereskin
I do not know how exactly you would integrate this additional image form MultiPost Thumbnails plugin.
You could use our built-in form builders to add a new product form- the actual coding would be up to you, but the form type is product_media_uploader or also file_uploader as seen in our wc-vendors-pro/public/class-wcvendors-pro-form-helper.php
Adding a field to the product page would be done similar to as in this example:
https://gist.github.com/fervous/048b04a4a73cde43fd77b34405917f54
Except you would be using the product_media_uploader or file_uploader field type instead of select/select2
Also as an example of how we use the file_upoader, see the code for the store icon uploader: wc-vendors-pro/public/forms/class-wcvendors-pro-store-form.php line 398