Add draft comments for MergeRequests

Implements a new model, DraftNote, which is related to MergeRequests
only and enables to comment on a review in batches. The DraftNotes are
only visible to the author until they're published at which point they
become regular Notes.

This also includes a DraftsController and two related services:
DraftNotes::CreateService and DraftNotes::PublishService

A DraftNote behaves almost identically to a Note, except has no cached
markdown fields and needs to process quick action changes every time it
is displayed.

NOTE: THIS IS ONLY THE BACKEND CHANGES. NO FRONTEND INCLUDED

1 files changed, 11 insertions, 0 deletions

diff --git a/config/routes/project.rb b/config/routes/project.rb
index fd12bb86946..79e93c04947 100644
--- a/config/routes/project.rb
+++ b/config/routes/project.rb
@@ -158,6 +158,17 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
         resources :approver_groups, only: :destroy
         ## EE-specific
 
+        ## EE-specific
+        scope module: :merge_requests do
+          resources :drafts, only: [:index, :update, :create, :destroy] do
+            collection do
+              post :publish
+              delete :discard
+            end
+          end
+        end
+        ## EE-specific
+
         resources :discussions, only: [:show], constraints: { id: /\h{40}/ } do
           member do
             post :resolve