Given a date in the format "YYYY-MM-DD", return the number of days left until the weekend.
- The weekend starts on Saturday.
- If the given date is Saturday or Sunday, return
"It's the weekend!".
- Otherwise, return
"X days until the weekend.", where X is the number of days until Saturday.
- If
X is 1, use "day" (singular) instead of "days" (plural).
- Make sure the calculation ignores your local timezone.