RFC 9567 error reporting agent demonstration

[ximon18]

Initial version of an RFC 9567 error report monitoring agent.

See the README for more introduction and usage.

Builds upon the existing introducing-idns branch of this project for compatability with the domain crate, https://github.com/NLnetLabs/domain for server functionality and https://github.com/NLnetLabs/daemonbase for process daemonisation.

Note: This code uses Tokio Tracing for logging with the intent that it would fit well with the Tokio Tracing logging emitted by the server functionality of the domain crate. However, when combined with daemonbase it's not clear to me how to leverage this properly. For example at present passing -v causes all levels of tracing logging within this new tool to be enabled at once irrespective of level, and at the same time no number of -v arguments cause the underlying domain crate server side logging to be emitted, at least not so far in my limited testing.

It currently lacks tests. It should at least have unit tests of the QNAME parsing, but I held off adding those yet as I'd like to know if the way I'm parsing the QNAME makes sense, or should I collect it to a Vec or even convert it to a string and parse it that way?

[ximon18]

If this were to be deployed on multiple servers the cookies need special attention m, e.g. to ensure they match on each server, plus there should be some mechanism to rotate them, etc, basically the guidelines in the cookie RFC should be taken into account.