Dynamic DNS RFC 2136 Support

[tynes]

I'd like to be able to dynamically update my zone file in a safe and secure way. Looking for prior art, I came across this RFC for Dynamic DNS - https://tools.ietf.org/html/rfc2136

Looking through the bns codebase, I didn't see any mentions of Dynamic DNS or ways to update the zone file dynamically without building a wrapper around the AuthServer and calling setFile with an updated zone file. This doesn't seem like the ideal solution.

RFC 2136 at least uses the DNS protocol itself to update the zone file, so that an additional HTTP server doesn't need to be ran. It also includes a permission system

the requestor's permission to update the RRs named in
the Update Section may be tested in an implementation dependent
fashion or using mechanisms specified in a subsequent Secure DNS
Update protocol. If the requestor does not have permission to
perform these updates, the server may write a warning message in its
operations log, and may either signal REFUSED to the requestor, or
ignore the permission problem and proceed with the update.

Supporting a very easy way for users to update their zone files is important for Handshake.