Fix group bot token name in REST API and GraphQL

What does this MR do and why?

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With https://gitlab.com/gitlab-org/security/gitlab/-/merge_requests/1993, group access token names became hidden from the REST API and GraphQL queries for all users.

This MR introduces an additional check so that users who can read_group can now read group bot names. This includes guests+ in a private group, and all users including non-members in a public group.

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app/serializers/member_entity.rb

@@ -40,9 +40,7 @@ class MemberEntity < Grape::Entity
 
   expose :valid_level_roles, as: :valid_roles
 
-  expose :user, if: -> (member) { member.user.present? } do |member, options|
-    MemberUserEntity.represent(member.user, options)
-  end
+  expose :user, if: -> (member) { member.user.present? }, using: MemberUserEntity
 
   expose :state