[7.x](backport #25219) Introduce httpcommon package in libbeat (add s…

…upport for Proxy) (#26587)

* Introduce httpcommon package in libbeat (add support for Proxy) (#25219)

(cherry picked from commit 4accfa8)

# Conflicts:
#	libbeat/monitoring/report/elasticsearch/config.go
#	metricbeat/module/elasticsearch/index/data_test.go

* Fix issues with backport.

* Fix changelog.

* FIx integration tests for ml-importer.

Co-authored-by: Steffen Siering <steffen.siering@elastic.co>
Co-authored-by: Blake Rouse <blake.rouse@elastic.co>
(cherry picked from commit 37e37f1)