User synchronization revamped.

code/MessengerApi/Models/UserIngestionOperation.cs

@@ -0,0 +1,21 @@
+using MessengerApi.Db;
+
+namespace MessengerApi.Models
+{
+    public class UserIngestionOperation
+    {
+        public UserIngestionOperationTypes Type { get; set; }
+
+        public UserIngestionOperationSubtypes Subtype { get; set; }
+
+        public string Username { get; set; }
+
+        public Action<MessengerDbContext> Operation { get; set; }
+
+        public override string ToString()
+        {
+            var value = $"Operation: {this.Type}/{this.Subtype} for {this.Username}.";
+            return value;
+        }
+    }
+}