Add publishing to openvsx

Author: cterry45

.github/workflows/prod_release.yml

@@ -115,3 +115,7 @@ jobs:
         run: npm run publish
         env:
           VSCE_PAT: ${{ secrets.VSCE_PAT }}
+      - name: Publish to Open VSX Registry
+        uses: HaaLeo/publish-vscode-extension@v2
+        with:
+          pat: ${{ secrets.OPEN_VSX_TOKEN }}