Ability to add custom Fulfillment text

[pierrefaure]

I need to add the tests but I'd need some directions about it.

I ran into a case where I needed both fulfillmentMessages and fulfillmentText so I thought submitting a PR would be a good idea.

[mattcarrollcode]

Thanks for the PR. What is your use case for both and different fulfillment text and fulfillment messages?

[pierrefaure]

We are doing this because we use Chatbase and our fulfillmentMessages is pretty complex to parse and might change in the future.

E.g. for now we have Text - Text - Payload - Text - Payload - Text

So by having fulfillmentText we can have a nice version of what we want to send to Chatbase for the transcript. + if we edit the order or add a new payload, it's way easier to just add the text we want to fulfillmentText.