Add a "Build Image" Github action

.github/workflows/docker-image.yml

@@ -0,0 +1,31 @@
+name: Docker Image CI
+
+on:
+  push:
+    branches: ["main"]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Get commit ID
+        id: vars
+        run: echo "sha_short=$(git rev-parse --short HEAD)" >> $GITHUB_OUTPUT
+      - name: Build and push Docker image
+        id: push
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: true
+          platforms: linux/amd64
+          tags: ghcr.io/diamondlightsource/dlstbx:latest,ghcr.io/diamondlightsource/dlstbx:${{ steps.vars.outputs.sha_short }}

Dockerfile

@@ -1,4 +1,4 @@
-FROM harbor.diamond.ac.uk/dockerhub-cache/dials/dials:latest
+FROM dials/dials:latest
 
 RUN yum install bzip2 libXxf86vm rrdtool git -y
 RUN pip install patchelf