Issue model: Add UserNotesCount property (#818)

Author: ivan-pavlik

NGitLab/Models/Issue.cs

@@ -76,4 +76,7 @@ public class Issue
 
     [JsonPropertyName("references")]
     public References References { get; set; }
+
+    [JsonPropertyName("user_notes_count")]
+    public int UserNotesCount { get; set; }
 }

NGitLab/PublicAPI.Unshipped.txt

@@ -2269,6 +2269,8 @@ NGitLab.Models.Issue.Title.get -> string
 NGitLab.Models.Issue.Title.set -> void
 NGitLab.Models.Issue.UpdatedAt.get -> System.DateTime
 NGitLab.Models.Issue.UpdatedAt.set -> void
+NGitLab.Models.Issue.UserNotesCount.get -> int
+NGitLab.Models.Issue.UserNotesCount.set -> void
 NGitLab.Models.Issue.WebUrl.get -> string
 NGitLab.Models.Issue.WebUrl.set -> void
 NGitLab.Models.Issue.Weight.get -> int?