Move email building to Azure Function.

[ob1dev]

Generation personalized email can take a while, therefore:

1. Create a new Azure Function.
2. Update Email Client to call Azure Function instead of Azure Logic App.
3. Move email building logic to the Azure Function.
4. Once Azure Function generates signup email, it should put it into Azure Queue Storage.
5. Update Azure Logic App to trigger on a new message in Azure Queue Storage.