Add Sidekiq job GC.stat :total_allocated_objects to structured logs

Follow up from #30286 (comment 257801314)

Perhaps we should focus on instrumenting jobs that are actually run in production? For example, Rails 6.0 started tracking object allocations (https://github.com/rails/rails/commit/42fec4b8de8c40d7778f936e200081c0dded1ed0) using GC.stat :total_allocated_objects. Maybe we should add that to structured logs?

We are using rails 5.2.3 today. This issue need be revisited when we migrate to Rails6.