dnsdist: Carry the exact incoming protocol (Do53, DNSCrypt, DoT, DoH) in DQ

[rgacogne]

Short description

This turned out to be more difficult than I expected. Part of the work already existed in #10338 but was not enough to be able to pass the right protocol to dnstap, which I wanted to do since it now supports DoT and DoH (updated dnstap.proto is included in this PR).

Fixes #10497.

I added the "backport to dnsdist-1.6.x" label because I think we need to fix the dnstap issue on that branch as well, but we clearly should not backport this PR. Perhaps a simple test on whether the request was received over DoH (dq.du is not nullptr) would be enough for 1.6.x?

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[omoerbeek]

Indeed much longer that you'd think. Anyway, looks good (with a few nits).