Break root hints data out from Perl module

[matsduf]

Root hints data is stored as a data section in Zonemaster/Engine/Recursor.pm. For some use cases it can be useful to be able to change that to private root hints data:

• DNS training using a private DNS tree including root and TLDs.
• Zonemaster unit tests making it possible to set up both parent and child in a private tree including TLDs.

To make these use cases possible, put the root hints data was a separate data file. Also make it possible to override that file with a private hints file without updating the perl code.

[mattias-p]

Ideally we should be keeping around a copy of named.root and parse that during initialization. Given that we can parse it in an acceptable fashion.

[matsduf]

Parsing as such should not be a problem, but keep keeping it in json format is not much extra work since it is not updated often. The question is rather how we are triggered to do the update.

[mattias-p]

If we keep it in its original format we could have a make target download the current version and diff it against our snapshot.
A possible downside to parsing the original format is that it could introduce additional dependencies.

Another possibility could be if IANA has a mailing list or something for announcements regarding the root hints file.

[matsduf]

Resolved by #1134