Use a separate feature flag to update query in members page

What does this MR do and why?

The new query introduced in !203506 (merged) that uses user_group_member_roles table when displaying member roles in members page caused an incident.

This MR introduces use_user_group_member_roles_members_page feature flag to revert back the query used in members page back to the original one without affecting other areas where use_user_group_member_roles feature flag is used (e.g. ee/app/models/preloaders/user_member_roles_in_groups_preloader.rb).

Summary

This MR updates ee/app/models/ee/member.rb to

      override :with_group_group_sharing_access
      def with_group_group_sharing_access(group)
        return super unless ::Feature.enabled?(:use_user_group_member_roles_members_page, ::Feature.current_request)

        #
        # This MR prevents execution of the following query
        #

        super.joins("LEFT OUTER JOIN user_group_member_roles ON members.user_id = user_group_member_roles.user_id \
          AND user_group_member_roles.group_id = group_group_links.shared_group_id \
          AND user_group_member_roles.shared_with_group_id = group_group_links.shared_with_group_id")
      end

References

https://gitlab.com/gitlab-org/gitlab/-/issues/575006+

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