[MM-51092] Automate release post for RCs and finals, include changelog (#2733)

.github/workflows/release.yaml

@@ -213,6 +213,6 @@ jobs:
           jq --null-input \
           --arg icon_url "https://mattermost.com/wp-content/uploads/2022/02/icon.png" \
           --arg username "MattermostRelease" \
-          --arg text "[$(jq -r .version package.json)] Release process for the desktop app ended, the new release can be found on [GitHub](https://github.com/mattermost/desktop/releases)." \
+          --arg text "$(bash -x scripts/generate_release_post.sh $(jq -r .version package.json))" \
           '{"username":$username,"icon_url": $icon_url, "text": $text }' > /tmp/webhook-data.json
           curl -i -H "Content-Type: application/json" -X POST -d @/tmp/webhook-data.json ${{ secrets.MM_DESKTOP_RELEASE_WEBHOOK_URL }} || echo "NOFICATION FAILED! check logs as this will succeed intentionally"