Allow functions to save files

[computationalmama]

Functions should be able to create files and output them to be downloadable content for the user.

• expose an API in gooey.ai/functions to be able to save a file. Since we use deno, we can consider https://docs.deno.com/examples/writing-files, but we can also consider the node API https://nodejs.org/en/learn/manipulating-files/writing-files-with-nodejs since it is widely known

• if the user saved a file in their js code, return the file data from functions/executor.js

• save the file data to gcs in functions recipe, save it as files: list[str] as a list of URLs

• display files to the user in the output column

• Make this work on integrations like whatsapp and web widget too

E.g. End-user workflow where this could be valuable - https://gooey.ai/doc-search/model-number-extraction-for-manuals-xluyas95mws4/