FIX: Add multisite support to Sidekiq::Pausable. (#6960)

Having a global Sidekiq pause switch is problematic because a site in
the cluster can pause Sidekiq for the entire cluster.

spec/components/sidekiq/pausable_spec.rb

@@ -1,36 +0,0 @@
-require 'rails_helper'
-require_dependency 'sidekiq/pausable'
-
-describe Sidekiq do
-  after do
-    Sidekiq.unpause!
-  end
-
-  it "can pause and unpause" do
-    Sidekiq.pause!
-    expect(Sidekiq.paused?).to eq(true)
-    Sidekiq.unpause!
-    expect(Sidekiq.paused?).to eq(false)
-  end
-
-  it "can still run heartbeats when paused" do
-    Sidekiq.pause!
-
-    freeze_time 1.week.from_now
-
-    jobs = Sidekiq::ScheduledSet.new
-
-    Sidekiq::Testing.disable! do
-      jobs.clear
-
-      middleware = Sidekiq::Pausable.new
-      middleware.call(Jobs::RunHeartbeat.new, { "args" => [{}] }, "critical") do
-        "done"
-      end
-
-      jobs = Sidekiq::ScheduledSet.new
-      expect(jobs.size).to eq(0)
-    end
-
-  end
-end