Delayed Job with priority greater than

Allows a user to create DelayedJobBackedUp and specify if they want to find jobs with a priority greater than the given priority.

Deploy Plan
-----------
> Does Infrastructure need to know anything special about this deploy?

Rollback Plan
-------------
* To roll back this change, revert the merge with: `git revert -m 1 MERGE_SHA` and perform another deploy.

URLs
----
> Links to bug tickets or user stories.

QA Plan
-------
> Fill in scenarios below. Review [QA Best Practices](https://source.sportngin.com/page/show/1227795-qa-best-practices).

Make sure the tests look okay and pass.
There is so much code duplication here, my eyes are bleeding... :feelsgood:

I think somethinkg like this would DRY it up a bit:

```ruby
def size
  if defined?(::Delayed::Backend::Mongoid::Job) && Delayed::Worker.backend == Delayed::Backend::Mongoid::Job
    query = greater_than_priority ? Delayed::Job.gte(priority: priority) : Delayed::Job.lte(priority: priority)
  else
    operator = greater_than_priority ? ">=" : "<="
    query = Delayed::Job.where("priority #{operator} ?", priority)
  end
  query.where(:locked_at => nil, :last_error => nil).count
end
```