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