Fix the namespaces of EE API LDAP entities

What does this MR do and why?

The MR moves all EE LDAP related entities that are in ee/lib/ee/api/entities/ to ee/lib/api/entities, and updates their namespace accordingly.

The fix is required to conform to the "Separation of EE code in the backend" rule for EE-only features. https://docs.gitlab.com/development/ee_features/#ee-only-features.

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Related to #263403