Make multistage Dockerfile self-contained (#9323)

Picking up all support files from the builder image has the advantage
that the Dockerfile is now fully selfcontained and can be also
run just standalone.

This allows also cross-compilation and pushing with the proper manifests
with Docker Buildkit:

```
docker buildx create --name xbuilder
docker buildx use xbuilder

docker buildx build -f Dockerfile.minio --platform linux/arm/v7,linux/amd64 --progress plain --push -t minio/minio .
```

which also has the advantage that the Dockerfile is the same
for all platforms.

Co-authored-by: Harshavardhana <harsha@minio.io>

Dockerfile

@@ -22,8 +22,8 @@ ENV MINIO_ACCESS_KEY_FILE=access_key \
 EXPOSE 9000
 
 COPY --from=0 /go/bin/minio /usr/bin/minio
-COPY CREDITS /third_party/
-COPY dockerscripts/docker-entrypoint.sh /usr/bin/
+COPY --from=0 /go/minio/CREDITS /third_party/
+COPY --from=0 /go/minio/dockerscripts/docker-entrypoint.sh /usr/bin/
 
 RUN  \
      apk add --no-cache ca-certificates 'curl>7.61.0' 'su-exec>=0.2' && \