Add v2 to reserved top level routes

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

db/post_migrate/20190325111602_rename_v2_root_namespaces.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class RenameV2RootNamespaces < ActiveRecord::Migration[5.0]
+  include Gitlab::Database::MigrationHelpers
+  include Gitlab::Database::RenameReservedPathsMigration::V1
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  # We're taking over the /v2 namespace as it necessary for Docker client to
+  # work with GitLab as Dependency proxy for containers.
+  def up
+    disable_statement_timeout do
+      rename_root_paths 'v2'
+    end
+  end
+
+  def down
+    disable_statement_timeout do
+      revert_renames
+    end
+  end
+end

doc/user/reserved_names.md

@@ -83,6 +83,7 @@ Currently the following names are reserved as top level groups:
 - unsubscribes
 - uploads
 - users
+- v2
 
 These group names are unavailable as subgroup names:
 

lib/gitlab/path_regex.rb

@@ -57,6 +57,7 @@ module Gitlab
       unsubscribes
       uploads
       users
+      v2
     ].freeze
 
     # This list should contain all words following `/*namespace_id/:project_id` in

spec/lib/gitlab/path_regex_spec.rb

@@ -100,7 +100,7 @@ describe Gitlab::PathRegex do
   end
 
   let(:ee_top_level_words) do
-    ['unsubscribes']
+    %w(unsubscribes v2)
   end
 
   let(:files_in_public) do