add cache for Buildah layers in GitHub Actions

- Configures cache for `/var/lib/containers/storage` using `actions/cache@v4`.
- Implements keys to reuse layers from previous builds.
- Enables layer reuse in Buildah with `layers: true`.

.github/workflows/build-ee.yml

@@ -42,6 +42,14 @@ jobs:
         with:
           platforms: all
 
+      - name: Cache Buildah layers
+        uses: actions/cache@v4
+        with:
+          path: /var/lib/containers/storage
+          key: ${{ runner.os }}-buildah-cache-${{ github.sha }}
+          restore-keys: |
+            ${{ runner.os }}-buildah-cache-
+
       - name: Buildah Action
         uses: redhat-actions/buildah-build@v2
         id: build-image
@@ -53,6 +61,7 @@ jobs:
           context: tools/execution_environments/ee-multicloud-public
           containerfiles: |-
             tools/execution_environments/ee-multicloud-public/Containerfile
+          layers: true
 
       -  name: Push To quay.io
          id: push-to-quay