[REQ] [RUBY] [FARADAY] Allow middleware to be configured

Created by: johngallagher

What and why

As a developer
Given I am generating a Ruby client
And I am using Faraday
When I configure the generated Ruby client
Then I expect to be able to add middleware in the configuration block
But I cannot
And I have to depend on ugly monkey patches
And that makes my code less reusable and less understandable

For more details, see this issue

Usage

PetstoreAPI.configure do |config|
  config.use :instrumentation, name: "request.faraday.petstore"
  config.request :retry, { retry_statuses: [429], max: 10 }
  config.server_index = nil
end

ActiveSupport::Notifications.subscribe(/request\.faraday.*/) do |name, starts, ends, _, env|
  $stdout.puts '<%s> [%s] %s (%.3f s)' % [name, env[:url].to_s, env[:method].to_s, ends - starts]
end

More details

• I'm borrowing Faraday's use, request and response syntax to specify the different middleware
• Then I'm forwarding these onto the connection
• I've tested this with clients I've generated locally and it works

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh

  Commit all changed files. This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master. These must match the expectations made by your contribution. You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*. For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master (5.3.0), 6.0.x
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.