Add 'acme-dns' to LetsEncrypt Add-on

The Let’s Encrypt add-on doesn’t have support for acme-dns. This is a self-hosted provider for the DNS-challenge.

Python already has a library for it:

I think adding this to the corresponding Dockerfile might be sufficient.

It would be awesome if you would consider it.

If you are really interested in this feature, then I suggest you vote for it yourself as a start. :wink: