Process form submission

[edgenard]

Write a function that processes the post request when form is submitted.

• It should be at the same path as the show_form function but use the HTTP method "POST"
• It should save the data in an S3 bucket
• The data should not be URL encoded or in Base64. It should be a plain string It's in JSON.
• The key pointing to each saved form submission should be unique
• Update the template stack outputs to reflect the changes made to the stack
• Show a page thanking the user for their submission