Adjust Content-Type header for Prometheus endpoint to include version

[Woutifier]

Prometheus v3 will, by default, be more strict about the content-types returned from scrape endpoints. With the current value (just text/plain), it would fail to scrape.

In this commit the value is changed from text/plain to text/plain; version=0.0.4.

See also [1] and [2]
[1] https://prometheus.io/docs/instrumenting/exposition_formats/ [2] https://prometheus.io/docs/prometheus/3.0/migration/

Short description

This closes #15071

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)

[miodvallat]

Looking good; version=0.0.4

[zeha]

Can we clarify this first please? #15071 (comment)

[coveralls]

Pull Request Test Coverage Report for Build 12889200336

Details

• 2 of 3 (66.67%) changed or added relevant lines in 3 files are covered.
• 46 unchanged lines in 11 files lost coverage.
• Overall coverage increased (+0.01%) to 64.709%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pdns/ws-auth.cc	0	1	0.0%

Files with Coverage Reduction	New Missed Lines	%
pdns/packethandler.cc	1	72.79%
modules/gpgsqlbackend/gpgsqlbackend.cc	1	88.62%
pdns/misc.cc	2	62.49%
pdns/backends/gsql/gsqlbackend.hh	2	97.71%
pdns/iputils.cc	3	56.07%
pdns/recursordist/recpacketcache.hh	3	89.55%
pdns/rcpgenerator.cc	3	90.37%
pdns/recursordist/test-syncres_cc1.cc	5	89.87%
pdns/signingpipe.cc	5	83.38%
pdns/dnsdistdist/dnsdist-carbon.cc	9	61.87%

Totals
Change from base Build 12884379895:	0.01%
Covered Lines:	127804
Relevant Lines:	166433

---

💛 - Coveralls