Extending DNS zone configuration in custom-hiera.yml

I’d like to enable notifications to DNS slave of a domain that is already defined through web UI by using also_notify parameter that dns::zone provides.

Expected outcome:

Relevant configuration generated to a named configuration files.

Foreman and Proxy versions:

Foreman and Proxy plugin versions:

Distribution and version:

Other relevant data:
What I’m trying achieve and possible solution was mentioned here and by @ekohl

and already asked by me in here: