refactor: create a redis service archetype
Required as part of #70 (closed)
Rebased on top of !4097 (merged)
This MR refactors the Redis service catalog definitions extracting common definitions into a single file.
This reduces the amount of copypasta definition, but also moves us towards building definitions for non-GitLab.com services in future, defined with alternative metric-catalogs.
cc @cmiskell
Edited by Andrew Newdigate