feat: implement example-go service with Docker support

- Add a new Makefile with build, docker-build, test, and clean targets, including cross-compilation support for Linux AMD64 and ARM64.
- Introduce a new Go executable `example-go` with a basic HTTP server setup.
- Create a new Dockerfile for an Alpine-based container including the `example-go` binary, with metadata labels and an entrypoint.

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

docker/Dockerfile

@@ -0,0 +1,21 @@
+FROM alpine:3.19
+
+ARG TARGETOS
+ARG TARGETARCH
+
+LABEL maintainer="Bo-Yi Wu <appleboy.tw@gmail.com>" \
+  org.label-schema.name="api" \
+  org.label-schema.vendor="Bo-Yi Wu" \
+  org.label-schema.schema-version="1.0" \
+  com.centurylinklabs.watchtower.stop-signal="SIGINT" \
+  io.containers.autoupdate="registry"
+
+RUN apk update && apk add --no-cache ca-certificates
+
+EXPOSE 8080
+
+ENV GODEBUG netdns=go
+
+COPY release/${TARGETOS}/${TARGETARCH}/example-go /bin/example-go
+
+ENTRYPOINT ["/bin/example-go"]