Add workflow step to build navigation2 (#126).

.github/workflows/docker-build.yml

@@ -39,3 +39,19 @@ jobs:
           docker load --input /tmp/moveit2.tar
           docker images
           cd space_robots && ./build.sh
+  space_nav2:
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Set up buildx
+        uses: docker/setup-buildx-action@v1
+      - name: Build space_nav2 image
+        uses: docker/build-push-action@v2
+        with:
+          context: navigation2
+          push: false
+          tags: osrf/space_nav2:latest
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+          no-cache: false