chore: moved some core interfaces into their own files

src/Pepperdash.Core/IKeyed.cs

@@ -0,0 +1,14 @@
+namespace PepperDash.Core
+{
+    /// <summary>
+    /// Unique key interface to require a unique key for the class
+    /// </summary>
+    public interface IKeyed
+	{
+        /// <summary>
+        /// Unique Key
+        /// </summary>
+		string Key { get; }
+    }
+
+}