Allow certain Sidekiq jobs to be throttled

## What does this MR do?

Allows certain slow running Sidekiq jobs to be throttled. It is disabled by default and can be enabled via the Application Settings. 

![Screen_Shot_2016-11-04_at_4.51.24_PM](/uploads/a1f1d24c693fcdb278602765cd404d94/Screen_Shot_2016-11-04_at_4.51.24_PM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG.md) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing

## What are the relevant issue numbers?

Related to #23352

See merge request !7292