Warn when releases have not been updated for a long time (#521)

Raise an alert during the daily auto-update about stale releases, e.g.:

- non-EOL releases with latest releases not updated in a year,
- non-EOL releases with a release date older than a year.

The threshold is configurable.

src/graalvm.py

@@ -23,7 +23,7 @@ with ProductData(config.product) as product_data:
 
         date_text = cells[date_index].get_text().strip()
         date = dates.parse_date(date_text)
-        if date > dates.today():
+        if date > dates.today_at_midnight():
             logging.info(f"Skipping future version {cells}")
             continue