Add permission for users to be able to administer their own contact form

Description of the need Contact Module

A site admin should have the ability to disallow users from turning on their personal contact form.

By default, users are not able to use individual contact forms in Backdrop CMS. But, as far as I can tell, there is no way for an admin to prevent users from enabling their own personal contact forms. I believe that this creates a situation in which users have the ability to enable personal contact forms, but no one is able to use them (other than admins, who could use them anyway).

I didn't test this as fully as I should. The issue came up in the forum: https://forum.backdropcms.org/forum/personal-contact-form-no-disable#com...

Proposed solution Add a permission "User may administer their own contact form." If this is permission is not available, then a user does not have the ability to enable or disable their personal contact form.

Additional information

To test this, you must enable the Contact module in core.