This PR awaits first a migration to Discord.

These actions allow 4 new notifications:

• when a new release of SOFA is done
• weekly to set up the SOFA dev meeting agenda
• weekly to summarize posts on GH discussions awaiting for a reply
• notification for all GH discussions "Announcements" or "Share your achievements"
• forward all GH notifications (PR, issues, stars) in a minimalist and visual way in the main channel
• rename existing actions to better identify/distinguish them all

Python API has been factorized to use mostly one script

By submitting this pull request, I acknowledge that
I have read, understand, and agree SOFA Developer Certificate of Origin (DCO).

Reviewers will merge this pull-request only if

• it builds with SUCCESS for all platforms on the CI.
• it does not generate new warnings.
• it does not generate new unit test failures.
• it does not generate new scene test failures.
• it does not break API compatibility.
• it is more than 1 week old (or has fast-merge label).