ci: use docker actions.

This allows us to use the GHA cache when building images, which should
speed up CI considerably, even without JOBS being set to the number of
processors on the machine, since the longest build step, epics-base,
changes the least often.

.github/workflows/base-image.yml

@@ -25,17 +25,21 @@ jobs:
       IMAGE: ${{ matrix.image.name }}
       SOURCE: https://github.com/${{ github.repository }}
     steps:
-      - uses: actions/checkout@v3
-      - name: Build image
-        run: cd ${{ matrix.image.dir }} && JOBS=$(nproc) docker compose build
+      - uses: actions/checkout@v4
+      - uses: docker/setup-buildx-action@v3
       - name: Log in to registry
         if: github.event_name == 'push' && vars.PUSH_TO_REGISTRY == 'true'
-        run: echo "${{ secrets.GITHUB_TOKEN }}" | docker login ghcr.io -u $ --password-stdin
-      - name: Push tagged image
-        if: github.event_name == 'push' && vars.PUSH_TO_REGISTRY == 'true' && github.ref_type == 'tag'
-        run: docker push $REGISTRY/$IMAGE:$TAG
-      - name: Push latest image
-        if: github.event_name == 'push' && vars.PUSH_TO_REGISTRY == 'true' && github.ref_type == 'branch'
-        run: |
-          docker tag $REGISTRY/$IMAGE:$TAG $REGISTRY/$IMAGE:latest
-          docker push $REGISTRY/$IMAGE:latest
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Build and push tagged image
+        uses: docker/bake-action@v4
+        with:
+          workdir: ${{ matrix.image.dir }}
+          files: docker-compose.yml
+          set: |
+            *.cache-from=type=gha,scope=${{ matrix.image.name }}
+            *.cache-to=type=gha,mode=max,scope=${{ matrix.image.name }}
+          push: ${{ github.event_name == 'push' && vars.PUSH_TO_REGISTRY == 'true' && github.ref_type == 'tag' }}