build: using cross compilation in docker build (#938)

Signed-off-by: Bin Du <bindu@microsoft.com>

Dockerfile

@@ -11,7 +11,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM docker.io/library/golang:1.20.2-alpine as builder
+FROM --platform=$BUILDPLATFORM docker.io/library/golang:1.20.2-alpine as builder
 ARG TARGETPLATFORM
 RUN apk add git make
 ENV ORASPKG /oras