perform_enqueued_jobs-like functionality

[yourtallness]

Hello,

Would it be possible to implement a perform_enqueued_jobs function like ActiveJob offers?

http://api.rubyonrails.org/v5.1/classes/ActiveJob/TestHelper.html#method-i-perform_enqueued_jobs

The purpose would be to check cases where we want to evaluate the actual results of the que job invocation.

Thank you in advance

[statianzo]

Sounds like a nice feature. Send a pull request and I'll give it a review.