[Amp story shopping] Support newlines in productDescription

[processprocess]

Add support for strings with \n such as:
"productDetails": "Lorem \n ipsum dolor sit amet consectetur adipisicing elit. \n Facere error d..."

[newmuis]

We should lightly process this in some way to avoid cases like "Hello\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\nWorld". We could regex replace multiple newlines down to ~one newline, and/or split on newlines discarding whitespace-only substrings, and/or make <p>'s out of each paragraph and not show empty ones.