Backport Gitaly dynamic timeouts from EE

EE added the ability to set timeouts when handling blobs. Since there's
no particular reason for this to be EE specific we can just backport
this to CE.

lib/gitlab/git/repository.rb

@@ -344,12 +344,12 @@ module Gitlab
         end
       end
 
-      def new_blobs(newrev)
+      def new_blobs(newrev, dynamic_timeout: nil)
         return [] if newrev.blank? || newrev == ::Gitlab::Git::BLANK_SHA
 
         strong_memoize("new_blobs_#{newrev}") do
           wrapped_gitaly_errors do
-            gitaly_ref_client.list_new_blobs(newrev, REV_LIST_COMMIT_LIMIT)
+            gitaly_ref_client.list_new_blobs(newrev, REV_LIST_COMMIT_LIMIT, dynamic_timeout: dynamic_timeout)
           end
         end
       end

lib/gitlab/gitaly_client/ref_service.rb

@@ -84,15 +84,22 @@ module Gitlab
         commits
       end
 
-      def list_new_blobs(newrev, limit = 0)
+      def list_new_blobs(newrev, limit = 0, dynamic_timeout: nil)
         request = Gitaly::ListNewBlobsRequest.new(
           repository: @gitaly_repo,
           commit_id: newrev,
           limit: limit
         )
 
+        timeout =
+          if dynamic_timeout
+            [dynamic_timeout, GitalyClient.medium_timeout].min
+          else
+            GitalyClient.medium_timeout
+          end
+
         response = GitalyClient
-          .call(@storage, :ref_service, :list_new_blobs, request, timeout: GitalyClient.medium_timeout)
+          .call(@storage, :ref_service, :list_new_blobs, request, timeout: timeout)
 
         response.flat_map do |msg|
           # Returns an Array of Gitaly::NewBlobObject objects