Avoiding make generate while updating feature categories

Part of gitlab-com/gl-infra/scalability#3400.

I came to realize that we'll invariably need to update the https://gitlab.com/gitlab-com/runbooks/-/blob/update-feat-categories-automation-avoid-make-generate/services/stage-group-mapping-crossover.jsonnet file when categories are updated and make generate needs to be executed afterwards, so it updates the recording rules appropriately.

Saying that, having the make update-feature-categories execute to open the MR is a waste that just delays the automation since we'll need to deal with it manually afterwards. This change focus on updating only the relevant files.