Restore Snap publish (#154)

.github/workflows/snap.yaml

@@ -33,3 +33,18 @@ jobs:
       with:
         name: micro-ros-agent-snap
         path: ${{ steps.build-snap.outputs.snap }}
+
+  publish:
+    if: github.ref == 'refs/heads/foxy' || startsWith(github.ref, 'refs/tags/')
+    runs-on: ubuntu-latest
+    needs: build
+    steps:
+    - uses: actions/download-artifact@v3
+      with:
+        name: micro-ros-agent-snap
+        path: .
+    - uses: snapcore/action-publish@v1
+      with:
+        store_login: ${{ secrets.STORE_LOGIN }}
+        snap: ${{needs.build.outputs.snap-file}}
+        release: ${{ startsWith(github.ref, 'refs/tags/') && 'candidate' || 'edge'}}