Support multiple email previews

[moshest]

Goals

We have emails with multiple states, such as plural and singular sentences and other states we want to test and see in our email previews.

Background

We are using the email dev tool to preview the email and test them before adding it to the product. Having multiple smaller states within each email making it harder to test each case.

Proposal

Change the PreviewProps object to support multiple previews by providing an array of props or even an object like: { props: Props, label: string }[] so we can view and send preview for each version before releasing.