Refactor for extension some add on related backend items
What does this MR do and why?
Refactor for extension some add on related backend items
- right now we would repeat a lot of setup code for introduction of a new add on like duo enterprise
- refactor these items in hopes that it will mean less setup code.
- broken off from !160106 (merged)
- see https://gitlab.com/gitlab-org/gitlab/-/issues/468050
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Related to #468050