Draft: Refactors EE logic out of CE context for user caps

What does this MR do and why?

We identified in that some EE specific code was accidentally setup in the CE context in this conversation: !75906 (comment 780025758)

The logic relates to validations/restrictions on the NamespaceSettings when SaaS user caps are enabled, but that feature is an EE-only/Gitlab.com-only feature

This MR refactors moves it into the EE context.

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