Add feature_category-label to grape metrics
What does this MR do?
This adds the feature_category
label to the metrics for grape
endpoints. This is needed so the metrics have the same labels as the
ones for controllers.
This also adds a spec so we don't forget about it in the future.
This label was added for controllers in !35281 (merged) for gitlab-com/gl-infra/scalability#386 (closed)
Edited by Bob Van Landuyt