feat(dnsdist): Add global ServerID

[pieterlexis]

Short description

This PR adds the option to set a stable "ServerID" for the running dnsdist instance by either using general.server_id in YAML or the (runtime) setServerID function. By default (and unset), the server's hostname is used.

Having this means that no matter how metrics, logs, or traces are sent to different collectors, they can always be attributed to a single dnsdist instance and hence, be correlated.

This ID can (for now) be used by Prometheus, Carbon, and remote logging. Once the structured logging PR (#16691) is merged, the ability to use this identifier in a log-field should be added.

This PR is an attempt to implement #16261.

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 21038114534

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

• 78 of 130 (60.0%) changed or added relevant lines in 8 files are covered.
• 13 unchanged lines in 6 files lost coverage.
• Overall coverage remained the same at 73.353%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pdns/dnsdistdist/dnsdist-configuration-yaml.cc	8	9	88.89%
pdns/dnsdistdist/dnsdist-actions-factory.cc	8	10	80.0%
pdns/dnsdistdist/dnsdist-lua-bindings.cc	1	3	33.33%
pdns/dnsdistdist/dnsdist-carbon.cc	8	11	72.73%
pdns/dnsdistdist/dnsdist-web.cc	32	50	64.0%
pdns/dnsdistdist/dnsdist-lua-actions.cc	15	41	36.59%

Files with Coverage Reduction	New Missed Lines	%
pdns/backends/gsql/gsqlbackend.hh	1	97.77%
pdns/misc.cc	1	61.34%
pdns/ueberbackend.cc	1	78.87%
pdns/recursordist/rec-eventtrace.hh	2	58.41%
pdns/recursordist/test-syncres_cc2.cc	3	89.18%
pdns/recursordist/test-syncres_cc1.cc	5	90.26%

Totals
Change from base Build 21037860535:	0.0%
Covered Lines:	129087
Relevant Lines:	165164

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💛 - Coveralls

[rgacogne]

Looks great, I have a couple nits but I love it!