Hi there,
It's an interesting workflow.
First thing to establish is if there is an endpoint for Google Analytics to accept an upload of a CSV file. It may well have it. More likely, however, it'll offer an API where you can update data, which may be what you need instead.
You can use appscripts to do something that responds to when there is a new row added, for sure. But to automate it you'll have to identify the endpoint on the other end, what does it need? Then it's a matter of shaping the data that you get when the user submits the form, to be in that format.
I found some example code that might get you started. It shows how to convert a range into CSV, and uploads it to google drive.