ci(workflow): add notify-github-discussion job

[ccamel]

Addresses axone-protocol/community#6.

• Additionally, removes Discord notifications on release, as GitHub Discussions will now serve as the primary release notification channel, with optional forwarding to Discord if needed.
• Also enables manual triggering with a specific tag input (only for the notification of release on discussions), alongside the default trigger on release. This adds flexibility for replaying the workflow when necessary.​

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

[bdeneux]

👍