build: Do not unnecessarily export images

When we do not require an image output from a `docker build` command,
we should not export an image as this just wastes time.

I believe this requires using buildx which can be enabled with
`docker buildx install`

Signed-off-by: Chris Crone <[email protected]>

Makefile

@@ -13,6 +13,7 @@
 #   limitations under the License.
 
 export DOCKER_BUILDKIT=1
+export BUILDX_NO_DEFAULT_LOAD=1
 
 UNAME_S := $(shell uname -s)
 ifeq ($(UNAME_S),Linux)