Add github action for rust build

.github/workflows/slackwatch.yml

@@ -0,0 +1,31 @@
+name: Build and Push Rust Docker Image
+
+on:
+  push:
+    branches:
+      - main
+      - dioxus-1
+    paths:
+      - 'backend/**'
+      - '.github/workflows/backend.yml'
+
+jobs:
+  build-and-push:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out the code
+        uses: actions/checkout@v2
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+
+      - name: Log in to GitHub Container Registry
+        run: docker login ghcr.io -u ${{ github.actor }} -p ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v2
+        with:
+          context: ./backend
+          file: ./backend/Dockerfile
+          push: true
+          tags: ghcr.io/slackspace-io/slackwatch:latest,ghcr.io/slackspace-io/slackwatch:dev,ghcr.io/slackspace-io/slackwatch:${{ github.sha }}