Write a function to sort a list of case files by date.
Use the signature def sort_case_files(case_files):. Each case file is a dictionary containing a date field formatted as YYYY-MM-DD. Return a new list ordered from earliest to latest date. Do not modify the input list. If two case files have the same date, preserve their original order.
date stringYYYY-MM-DD formatdef sort_case_files(case_files):