Allow use of Faraday v2
This will enable GitLab Omnibus to use Bundler to install its gems. Currently gitlab-exporter is locked to Faraday 1.8, but Omnibus GitLab locks to Faraday v2.8.1.
We currently lock to Faraday v2.8.1 to avoid a RubyGems issue loading the net-http default gem. This will be fixed in RubyGems 3.5.5: https://github.com/rubygems/rubygems/issues/7374
The Elasticsearch probe uses Faraday to perform HTTP GET requests, and there should be no change needed: https://github.com/lostisland/faraday/blob/main/UPGRADING.md
Relates to gitlab-org/omnibus-gitlab#8368