Add workflow to trigger Docker publish on release

Introduces a GitHub Actions workflow that triggers the NapCat-Docker docker-publish workflow when a release is published. This automates Docker image publishing upon new releases.

.github/workflows/trigger-docker-publish.yml

@@ -0,0 +1,19 @@
+name: Trigger Docker Publish on Release
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  shell-docker:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Trigger NapCat-Docker docker-publish workflow
+        env:
+          GH_TOKEN: ${{ secrets.NAPCAT_BUILD }}
+        run: |
+          curl -X POST \
+            -H "Accept: application/vnd.github+json" \
+            -H "Authorization: Bearer $GH_TOKEN" \
+            https://api.github.com/repos/NapNeko/NapCat-Docker/actions/workflows/docker-publish.yml/dispatches \
+            -d '{"ref":"main"}'