Load the Sidekiq client tracer on Sidekiq server

[MXfive]

Instrument the Sidekiq client when running a Sidekiq server, Sidekiq jobs can schedule other jobs.

See documentation here: https://github.com/mperham/sidekiq/wiki/Middleware#client-middleware-registered-in-both-places

[delner]

@MXfive Looks good to me! We need to get CI to pass before we merge this. Looks like an unrelated issue with Excon might be causing the failures. Once we have that fixed, you'll need to rebase.

[marcotc]

Hey @MXfive, you can now rebase with master and the excon CI error should be gone.

Also, could you add a test to assert that these changes are working correctly?
I suggest creating a worker class that schedules another job, similar to how we test our ErrorWorker, for example:

dd-trace-rb/test/contrib/sidekiq/server_tracer_test.rb

Lines 12 to 18 in d0c26ec

	class ErrorWorker
	include Sidekiq::Worker
	def perform
	raise TestError, 'job error'
	end
	end

[MXfive]

@marcotc Sure I will have a go at adding test coverage this weekend. Still looks like jruby tests is broken though for changes unrelated to this.

[marcotc]

👋 @MXfive, I've recently merged #1092, which migrated our Sidekiq tests from Minitest to RSpec, so testing should be much easier now.

[DocX]

Is this not a duplicate of #1099 ?

[marcotc]

Well noted @DocX, I'm going to close this issue as it had been addressed by #1099. Thank you for you work here @MXfive, the changes will be shipped on next release.