Remove the use of hardcoded special "strings" in the UI for special approval rules like "License-Check" and "Vulnerbility-Check"

Context:

As part of https://gitlab.com/gitlab-org/gitlab-ee/issues/13067 and https://gitlab.com/gitlab-org/gitlab-ee/issues/9928 we have conditional logic to match on specific strings in the frontend. (a specific approval rule).

If we have a match we do things like show rule specific tooltips and enable different behavior in the merge request widget or the license management area.

If we add additional rules in the future, we should define an approach where these special rules are defined as a constant in the backend and passed through the frontend.

Right now we will run into the issue of hardcoding those values in the frontend, and they may become out of sync.