Follow-up from "Endpoint for creating custom dashboard"

The following discussion from !212034 should be addressed:

• @DylanGriffith started a discussion:

  Nitpick (non-blocking): There's some mention at https://docs.gitlab.com/development/feature_flags/#current-request-actor that we try to avoid using no actor. We can do a little better here with:

            ::Feature.enabled?(:custom_dashboard_storage, Feature.current_request)

  Anyway I don't really consider this blocking because I doubt you're planning on doing a percentage based rollout of this feature flag.