feat(dnsdist): Add instance field to OT Trace messages

[pieterlexis]

Short description

This PR ensures there is an instance field set to the DNSDist server id in OpenTelemetry Trace messages.

Checklist

I have:

• read the CONTRIBUTING.md document
• read and accepted the Developer Certificate of Origin document, including the AI Policy, and added a "Signed-off-by" to my commits
• 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)

[coveralls]

Pull Request Test Coverage Report for Build 21166342258

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 10936 unchanged lines in 105 files lost coverage.
• Overall coverage decreased (-4.9%) to 67.847%

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Files with Coverage Reduction	New Missed Lines	%
pdns/protozero-trace.hh	1	67.77%
pdns/burtle.hh	2	97.59%
pdns/channel.hh	2	47.48%
pdns/dns.cc	2	87.39%
pdns/dnsdistdist/dnsdist-lua-bindings-kvs.cc	2	0.0%
pdns/dnsdistdist/dnsdist-lua.hh	2	0.0%
pdns/dnsdistdist/dnsdist-opentelemetry.cc	2	94.47%
pdns/epollmplexer.cc	2	83.85%
pdns/libssl.hh	2	0.0%
pdns/pollmplexer.cc	2	84.31%

Totals
Change from base Build 21142287425:	-4.9%
Covered Lines:	105792
Relevant Lines:	146927

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💛 - Coveralls