User Mapping - API Development (GraphQL)

On this issue, we will work on creating the GraphQL endpoints that will be used by the improved user mapping.

Two types of users will interact with the feature: group owners and assigned users.

Initially, group owners will use the User reassignment UI, which will be supported by the GraphQL endpoints created here.

Group owners will be able to list all import source users and reassign a real user to a source user. They can also cancel that reassignment if needed. This endpoint must:

• Only be accessible to group owners.
• Return paginated Import::SourceUser records
• Include a mutation for assigning a real user to an Import::SourceUser
• Include a mutation to revoke the assignment of a user from an Import::SourceUser
• Include a mutation to keep as a placeholder user

Note: These endpoints should only be available when the feature flag improved_user_mapping is enabled.

Questions: Should the email actions also be accessible via these endpoints?