Add LUA Record support

[larsl-net]

Is your feature request related to a problem? Please describe.
I am working on the migration of my PowerDNS managed zones to dnscontrol. Currently, I run in the problem that the LUA Records which I use result in an error, because they are not supported.

dnscontrol preview --domains example.com      
******************** Domain: example.com
ERROR
Error getting corrections (powerdns): unknown rtype (LUA) when parsing (A "ifportup(443, {'1.1.1.1', '1.2.3.4'},{selector='all'})") domain=(example.com)
Done. 0 corrections.
completed with errors

Describe the solution you'd like
Add support for LUA records

Describe alternatives you've considered
A way to ignore records with an unsupported record type.

Additional context
Official docs from PowerDNS
https://doc.powerdns.com/authoritative/lua-records/

[tlimoncelli]

CC @jpbede