Add static entries to dynamic zones

[ericbaum]

It would be interesting to have the capability of adding some static entries to zones configured as "dynamic". If we try to do it in the way things are right now we end up with a concat::fragment error as the concat was not initialized for the dynamic zone.

[cjeanneret]

Hello,

the main issue with that feature is the bind management for the dynamic zones: we have to freeze it, edit it, thaw it and then notify, with a new serial.
None of that logic is present in the module… And, tbh, I don't think we'll have time to do that (this would require native types in order to wrap rndc commands) :/.

Care to do some PR on your own?