Natively support the %Y/%m/%d date format

For parsing dates such as 2020/01/25, as seen on https://github.com/envoyproxy/envoy/blob/main/RELEASES.md#major-release-schedule.

src/common/dates.py

@@ -12,6 +12,7 @@ def parse_date(text: str, formats: list[str] = frozenset([
     "%d-%B-%Y",  # 1-January-2020
     "%Y-%m-%d",  # 2020-01-01
     "%m/%d/%Y",  # 01/25/2020
+    "%Y/%m/%d",  # 2020/01/25
 ])) -> datetime:
     """Parse a given text representing a date using a list of formats.
     """