Implement PatternAsFile for StringMatcher (#651)

src/WireMock.Net/Models/StringPattern.cs

@@ -0,0 +1,18 @@
+namespace WireMock.Models
+{
+    /// <summary>
+    /// StringPattern which defines the Pattern as a string, and optionally the filepath pattern file.
+    /// </summary>
+    public struct StringPattern
+    {
+        /// <summary>
+        /// The pattern as string.
+        /// </summary>
+        public string Pattern { get; set; }
+
+        /// <summary>
+        /// The filepath (optionally)
+        /// </summary>
+        public string PatternAsFile { get; set; }
+    }
+}