Update milestone plan script to work with the new release schedule
We need to update the script as it currently reads from the now removed release_dates.json
file.
New releases starting from 16.6 will happen on the 3rd Thursday of the month. The file we should read from is now https://gitlab.com/gitlab-com/www-gitlab-com/-/raw/master/data/releases.yml.
When the script is fixed, we should also update the scheduled pipeline cron. The pipeline is currently scheduled to run at 12:00am on the 10th. Since the 3rd Thursday would fall between the 15th and the 21th, we could make it run at the end of the month to give us some time to prepare, or run it on the 1st.
Edited by Achilleas Pipinellis