Raw XML POST not working in V2, V3 and V4. Added test for simple POST interaction with different content types.

tests/PactNet.Tests/TestXmlRequestBody.cs

@@ -0,0 +1,39 @@
+using System.Net;
+using System.Net.Http;
+using System.Text;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace PactNet.Tests
+{
+    public class TestXmlRequestBody
+    {
+        [Theory]
+        [InlineData("AnyText", "text/plain")]
+        [InlineData(@"{ ""simple"":""json"" }", "application/json")]
+        [InlineData("<?xml version='1.0'?><rootNode><rootNode/>", "application/xml")]
+        public async Task Post_simple_request_content(string body, string contentType)
+        {
+            // Arrange: Define simple POST interaction
+            var pactBuilder = Pact.V3("consumer", "provider").WithHttpInteractions();           
+            pactBuilder
+                .UponReceiving("any description")
+                .Given("any given")
+                    .WithRequest(HttpMethod.Post, "/any/endpoint")
+                    .WithBody(body, contentType)
+                .WillRespond()
+                    .WithStatus(HttpStatusCode.OK);
+
+            await pactBuilder.VerifyAsync(async ctx =>
+            {
+                // Act: Make POST request with the same body and content type
+                var client = new HttpClient();
+                client.BaseAddress = ctx.MockServerUri;
+                var something = await client.PostAsync("/any/endpoint", new StringContent(body, Encoding.UTF8, contentType));
+
+                // Assert
+                Assert.True(something.IsSuccessStatusCode);
+            });
+        }
+    }
+}