Fix Dockerfile build and zlib vulnerability

- Add missing build step to compile Go binary in build stage
- Use CGO_ENABLED=0 for static binary compatible with Alpine
- Upgrade base image from alpine:3 to alpine:3.23 to fix zlib out-of-bounds write vulnerability

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: andreeaalexandra

Dockerfile

@@ -7,9 +7,14 @@ RUN yum install -y  \
       bash \
       go
 
-FROM alpine:3
+WORKDIR /build
+COPY . .
+RUN CGO_ENABLED=0 go build -o /bin/aws-sigv4-proxy .
+
+FROM alpine:3.23
+
 COPY --from=build /etc/ssl/certs/ca-bundle.crt /etc/ssl/certs/
-COPY --chmod=755 bin/aws-sigv4-proxy /aws-sigv4-proxy
+COPY --from=build /bin/aws-sigv4-proxy /aws-sigv4-proxy
 COPY entrypoint.sh /entrypoint.sh
 
 ENTRYPOINT ["/entrypoint.sh"]