ruby: Add convenient construction of rawPayload messages

ruby/lib/svix/message_api.rb

@@ -22,4 +22,33 @@ def expunge_content(app_id, msg_id)
       return @api.v1_message_expunge_content(app_id, msg_id)
     end
   end
+
+  # Creates a [`MessageIn`] with the payload already being serialized.
+  #
+  # The payload is not normalized on the server (usually whitespace outside
+  # of string literals, unnecessarily escaped characters in string and such
+  # are fixed up by the server), and is not even required to be JSON.
+  #
+  # `attributes[:payload]` must be a string. An extra attribute `content_type`
+  # is accepted that sets the `content-type` header of the payload, overwriting
+  # the default of `application/json` if specified. Other than that, the
+  # attributes are forwarded [`MessageIn.new`], so all the same ones are
+  # accepted.
+  def message_in_raw(attributes = {})
+    if !attributes.key?(:transformations_params)
+      attributes[:transformations_params] = {}
+    end
+    attributes[:transformations_params][:rawPayload] = attributes[:payload]
+    attributes[:payload] = {}
+
+    content_type = attributes.delete(:content_type)
+    if content_type != nil
+      if !attributes[:transformations_params].key?(:headers)
+        attributes[:transformations_params][:headers] = {}
+      end
+      attributes[:transformations_params][:headers][:'content-type'] = content_type
+    end
+
+    return MessageIn.new(attributes)
+  end
 end