JSON file exporting Feedback 3 submissions should have "final" in the filename, not "midpoint"

[contraexemplo]

We have to export a JSON file with feedback submissions to authorize stipend payments. Software Freedom Conservancy expects the file for Feedback 3 submissions to be named outreachy-round-YYYY-internship-round-final-feedback.json. Our website currently creates a file named outreachy-round-YYYY-internship-round-midpoint-feedback.json.

We need to make it so files exporting Feedback 3 submissions are automatically named outreachy-round-YYYY-internship-round-final-feedback.json.

[iamjaysingh]

Hi! I'm interested in working on this bug. If no one is currently working on it, I'd like to take it and submit a pull request.