Follow-up from "Geo: make console messages consistent"

The following discussion from !16584 (merged) should be addressed:

• @mkozono started a discussion: (+1 comment)

  I think it would be nice to align the endpoints further by reusing a shared message entity i.e. pulling the Message entity out of the InternalPostReceive module to be on its own:

      class ConsoleMessage < Grape::Entity
        expose :message
        expose :type
      end

  Do you think that direction makes sense (for later)?

  I assume you saw the basic/alert message type names and prefer info/warning. I think I agree. Annoyingly it will take a backwards-compatible Gitaly release and then next Rails release to change those types.