Add HTTP headers support to common HTTP client.

[roidelapluie]

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This is named http_headers so it does not clash with blackbox exporter's headers and Prometheus remote client's headers, which are simple maps.

Signed-off-by: Julien Pivotto [email protected]

[roidelapluie]

Mailing list discussion: https://groups.google.com/g/prometheus-developers/c/p9HTlPzwUEo

[jeromeinsf]

Wondering if this will enable what was intended in https://github.com/prometheus/common/pull/326

[zetaab]

@roidelapluie @LeviHarrison what is status in this PR? At least I am interested of this feature

[Dronec]

Me too! Adding headers to requests is a relatively trivial operation and multiple APIs support that

[LeviHarrison]

Just some small revisions

@roidelapluie friendly ping

[roidelapluie]

@LeviHarrison here you go 🙂

[pracucci]

@roidelapluie I think this PR introduced an issue in JSON marshalling. Could you take a look at https://github.com/prometheus/common/pull/651 please?

[udf2457]

@roidelapluie any chance you could update the docs to reflect the existence of http_headers ?

CTRL-F of the docs yields zero results for http_headers

[roidelapluie]

https://github.com/prometheus/prometheus/pull/14660/files