Port GL code for urgency setting for Rails controllers

Problem

CDot lacks ability to set urgency on controller. urgency is available in gitlab repo to allow devs to specify a fairer expectation of acceptable request duration. This means our APDEX scores are less useful, treating low and hight priorities as the same.

Currently on CDot, I think any request taking more than 0.4 seconds are counted as failure.

This will help #4884 (closed)

We ported feature categorization earlier, and this will be build on top of that.

Proposal

We need to port GitLab's urgency setting over, so we can set different urgency on different controllers.

Result

More useful APDEX score

Next steps (if any)

How will we measure success?