trace: support DNS protocol

[achille-roussel]

When inspecting network traffic with timecraft trace request, it would be useful to have DNS requests and responses displayed. It is even more important now that Go guests may use net.Resolver which is going to send DNS queries over UDP sockets (see dispatchrun/net#16).

We do not yet have a precedent for managing datagram messages in internal/debug/tracing, so a major part of this work will be figuring out how to do that and whether the abstractions we have in place need to be modified to support this use case.