Add dispatch to central jellyfin-plugins on release

After each successful release to gh-pages, triggers a repository_dispatch
to LuckyNoS7evin/jellyfin-plugins to rebuild the combined manifest.
Requires JELLYFIN_PLUGINS_DISPATCH_TOKEN secret (PAT with public_repo scope).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: LuckyNoS7evin

.github/workflows/publish.yml

@@ -136,3 +136,15 @@ jobs:
           git add manifest.json releases/
           git diff --staged --quiet || git commit -m "Release $VERSION"
           git push origin gh-pages
+
+      - name: Trigger central manifest update
+        if: ${{ secrets.JELLYFIN_PLUGINS_DISPATCH_TOKEN != '' }}
+        env:
+          JELLYFIN_PLUGINS_DISPATCH_TOKEN: ${{ secrets.JELLYFIN_PLUGINS_DISPATCH_TOKEN }}
+        run: |
+          curl -X POST \
+            -H "Authorization: Bearer $JELLYFIN_PLUGINS_DISPATCH_TOKEN" \
+            -H "Accept: application/vnd.github+json" \
+            -H "X-GitHub-Api-Version: 2022-11-28" \
+            https://api.github.com/repos/LuckyNoS7evin/jellyfin-plugins/dispatches \
+            -d '{"event_type":"plugin-published","client_payload":{"plugin":"missing-episodes"}}'