Thread-safe Audited.without_auditing

[dleavitt]

Currently there's no way to disable all auditing for a block, e.g.

Audited.without_auditing do
  # something that changes a lot of records
  record.deep_duplicate_with_all_associations
end

I'm guessing this is because it wouldn't be thread-safe. The per-class equivalent solves this by using a thread-local variable.

Would you be open to a PR that adds similar behavior to the global setting?

[Aesthetikx]

I would also like this, for example wrapping a long-running job that does not need auditing for the duration and context of that job.