[DevOps Adoption] Improve table sorting

Sorting arrow feels the wrong way around, i.e., down should indicate a→z.

This should be aligned with gitlab-ui#1430 (closed) and #330478 (comment 571642492) from VSA.

Iterations

1. Hover background - this should be the quickest to implement because we can just align with @ameliabauerly's design
2. Arrow color - this should be relatively quick but I need to check with the UX foundations team and document in PJs
3. Arrow position - this will be more complex to implement