feature: supports adding custom LFS track pattern

src/ViewModels/LFSTrackCustomPattern.cs

@@ -0,0 +1,43 @@
+using System.ComponentModel.DataAnnotations;
+using System.Threading.Tasks;
+
+namespace SourceGit.ViewModels
+{
+    public class LFSTrackCustomPattern : Popup
+    {
+        [Required(ErrorMessage = "LFS track pattern is required!!!")]
+        public string Pattern
+        {
+            get => _pattern;
+            set => SetProperty(ref _pattern, value, true);
+        }
+
+        public bool IsFilename
+        {
+            get;
+            set;
+        } = false;
+
+        public LFSTrackCustomPattern(Repository repo)
+        {
+            _repo = repo;
+            View = new Views.LFSTrackCustomPattern() { DataContext = this };
+        }
+
+        public override Task<bool> Sure()
+        {
+            _repo.SetWatcherEnabled(false);
+            ProgressDescription = "Adding custom LFS tracking pattern ...";
+
+            return Task.Run(() =>
+            {
+                var succ = new Commands.LFS(_repo.FullPath).Track(_pattern, IsFilename);
+                CallUIThread(() => _repo.SetWatcherEnabled(true));
+                return succ;
+            });
+        }
+
+        private readonly Repository _repo = null;
+        private string _pattern = string.Empty;
+    }
+}