Add rake task to gather `GC.stat` for Sidekiq.

lib/tasks/gc.rake

@@ -0,0 +1,21 @@
+desc "Returns `GC.stat` for each Sidekiq process in JSON"
+task "sidekiq:gc_stat" do
+  pids = `ps -eo pid,args | grep ' [s]idekiq ' | awk '{print $1}'`.split("\n").map(&:to_i)
+  results = []
+  hostname = `hostname`.chomp
+
+  pids.each do |pid|
+    tmp_path = Tempfile.new.path
+
+    system(
+      "bundle exec rbtrace -p #{pid} -e \"o = GC.stat; f = File.open('#{tmp_path}', 'w'); f.write(o.to_json); f.close\"",
+      out: "/dev/null", err: "/dev/null"
+    )
+
+    result = JSON.parse(File.read(tmp_path))
+    result["hostname"] = hostname
+    results << result
+  end
+
+  puts results.to_json
+end