fix: use reproducible-containers/buildkit-cache-dance to cache llm-d builds

Signed-off-by: Nick Mitchell <nickm@us.ibm.com>

Author: starpit

.github/workflows/llm-d-image-build.yml

@@ -8,8 +8,8 @@ on:
 # for debugging
 #  push:
 #    branches: [ main ]
-#  pull_request:
-#    branches: [ main ]
+  pull_request:
+    branches: [ main ]
 
 # cancel any prior runs for this workflow and this PR (or branch)
 concurrency:
@@ -67,8 +67,24 @@ jobs:
         run: git clone https://github.com/llm-d/llm-d.git -b $LLMD_VERSION
 
       - name: Set up Docker Buildx
+        id: setup-buildx        
         uses: docker/setup-buildx-action@v3
 
+      - name: Cache
+        uses: actions/cache@v4
+        id: cache
+        with:
+          path: cache-mount
+          key: cache-mount-${{ hashFiles('llm-d/docker/Dockerfile.cuda') }}
+
+      - name: Restore Docker cache mounts
+        uses: reproducible-containers/buildkit-cache-dance@v3
+        with:
+          builder: ${{ steps.setup-buildx.outputs.name }}
+          cache-dir: cache-mount
+          dockerfile: llm-d/docker/Dockerfile.cuda
+          skip-extraction: ${{ steps.cache.outputs.cache-hit }}
+
       # We only need to log in if we are going to push
       - name: Login to Container Registry
         uses: docker/login-action@v3