Allow submissions to be ordered by stage

[NateWr]

Describe the problem you would like to solve
Editors want to be able to order the submissions by stage, so that they can more easily organize and track their submissions.

Describe the solution you'd like
In the new submissions table (#8880), it should be possible to click the Stage column header to order submissions by the current workflow stage.

The /submissions?orderBy= param in the REST API should support a value of stage.

Who is asking for this feature?
This request came out of user research for the new submissions list (#7495).