dnsdist: add support for dnstap new http_protocol field

[chbruyand]

Short description

This fix #15108

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)

[rgacogne]

Looks good, great work!

[coveralls]

Pull Request Test Coverage Report for Build 13306660380

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 14 of 18 (77.78%) changed or added relevant lines in 2 files are covered.
• 50 unchanged lines in 13 files lost coverage.
• Overall coverage decreased (-0.006%) to 64.711%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pdns/dnsdistdist/dnsdist-actions-factory.cc	11	15	73.33%

Files with Coverage Reduction	New Missed Lines	%
modules/gpgsqlbackend/gpgsqlbackend.cc	1	88.62%
pdns/dnsdistdist/dnsdist-backend.cc	1	66.19%
pdns/pollmplexer.cc	1	83.66%
pdns/backends/gsql/gsqlbackend.hh	2	97.71%
pdns/communicator.cc	3	71.85%
pdns/recursordist/syncres.cc	3	80.21%
pdns/iputils.hh	3	78.23%
pdns/iputils.cc	3	56.99%
pdns/communicator.hh	3	77.78%
pdns/signingpipe.cc	5	84.45%

Totals
Change from base Build 13305454892:	-0.006%
Covered Lines:	128172
Relevant Lines:	167040

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💛 - Coveralls

[rgacogne]

A small nit from clang-tidy and this should be good to go :)