Correlation id as a custom type (#13)

Co-authored-by: Philip Pålsson <philip.palsson@insurello.se>

Author: emilklasson

src/Insurello.RabbitMqClient/MqClient.fs

@@ -52,8 +52,12 @@ module MqClient =
         | Json of string
         | Binary of byte array
 
+    type CorrelationId =
+        | Generate
+        | Id of string
+
     type PublishMessage =
-        { CorrelationId: string
+        { CorrelationId: CorrelationId
           Headers: Map<string, string>
           Content: Content }
 
@@ -431,7 +435,10 @@ module MqClient =
                                      (ContentType = contentTypeStringFromContent message.Content,
                                       Persistent = true,
                                       MessageId = messageId,
-                                      CorrelationId = message.CorrelationId,
+                                      CorrelationId =
+                                          (match message.CorrelationId with
+                                           | Generate -> ""
+                                           | Id correlationId -> correlationId),
                                       Headers =
                                           (message.Headers
                                            |> Map.map (fun _ v -> v :> obj)