It may not be the best place for that (gha.py would have been better), but it's the shorter / faster way to do it for now.
Moreover it now uses logging for writing the group. The logger format has been updated for this to work. This was done to fix issues on GitHub Action logs, where groups were declared after the logs.
Create common functions parse_date, parse_month_year_date and parse_datetime.
Those functions support trying multiple formats, and come with default formats lists that support most of the date format encountered so far.
Notable change: year-month dates are now set to the end of month (impacted couchbase-server and ibm-aix).
