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/multisite/pausable_spec.rb

@@ -0,0 +1,89 @@
+require 'rails_helper'
+require_dependency 'sidekiq/pausable'
+
+RSpec.describe "Pausing/Unpausing Sidekiq", type: :multisite do
+  after do
+    $redis.flushall
+  end
+
+  describe '#pause!, #unpause! and #paused?' do
+    it "can pause and unpause" do
+      Sidekiq.pause!
+      expect(Sidekiq.paused?).to eq(true)
+
+      test_multisite_connection('second') do
+        expect(Sidekiq.paused?).to eq(false)
+      end
+
+      Sidekiq.unpause!
+
+      expect(Sidekiq.paused?).to eq(false)
+
+      test_multisite_connection('second') do
+        Sidekiq.pause!
+        expect(Sidekiq.paused?).to eq(true)
+      end
+    end
+  end
+end
+
+RSpec.describe Sidekiq::Pausable do
+  after do
+    $redis.flushall
+  end
+
+  it "can still run heartbeats when paused" do
+    Sidekiq.pause!
+
+    freeze_time 1.week.from_now
+
+    jobs = Sidekiq::ScheduledSet.new
+    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
+
+  describe 'when sidekiq is paused', type: :multisite do
+    let(:middleware) { Sidekiq::Pausable.new }
+
+    def call_middleware(db = RailsMultisite::ConnectionManagement::DEFAULT)
+      middleware.call(Jobs::PostAlert.new, {
+        "args" => [{ "current_site_id" => db }]
+      }, "critical") do
+        yield
+      end
+    end
+
+    it 'should delay the job' do
+      Sidekiq.pause!
+
+      called = false
+      called2 = false
+      call_middleware { called = true }
+
+      expect(called).to eq(false)
+
+      test_multisite_connection('second') do
+        call_middleware('second') { called2 = true }
+        expect(called2).to eq(true)
+      end
+
+      Sidekiq.unpause!
+      call_middleware { called = true }
+
+      expect(called).to eq(true)
+
+      test_multisite_connection('second') do
+        Sidekiq.pause!
+        call_middleware('second') { called2 = false }
+        expect(called2).to eq(true)
+      end
+    end
+  end
+end