build: support multi-architecture builds in Dockerfile

Add ARG directives for TARGETOS and TARGETARCH to enable 
multi-architecture support. Modify the build command to 
use the specified target OS and architecture for more 
flexible and portable builds. Ensure compatibility 
with different deployment environments.

Dockerfile

@@ -4,6 +4,9 @@ ADD go.* /build
 RUN go mod download
 
 FROM deps as build
+ARG TARGETOS
+ARG TARGETARCH
+
 ENV CGO_ENABLED=0
 ADD . /build
 RUN if [ $(go mod tidy -v 2>&1 | grep -c unused) != 0 ]; then echo "Unused modules, please run 'go mod tidy'"; exit 1; fi
@@ -14,7 +17,7 @@ RUN ["/bin/bash", "-c", "cat coverage.txt.tmp | grep -v -f <(find . -type f | xa
 RUN go tool cover -html=coverage.txt -o coverage.html
 RUN go tool cover -func=coverage.txt
 RUN rm coverage.txt.tmp
-RUN GOOS=linux GOARCH=amd64 CGO_ENABLED=0 go build -mod=readonly -o release/default-request-adder -ldflags '-w -s'
+RUN GOOS=${TARGETOS} GOARCH=${TARGETARCH} CGO_ENABLED=0 go build -mod=readonly -o release/default-request-adder -ldflags '-w -s'
 
 FROM scratch as export
 COPY --from=build /build/coverage.txt /