[docker] security fix of sudo/chown/user issue #1638 (#1639)

## Summary
Potential fix of mentioned security issue:
#1638

## How was it tested?
devbox generate dockerfile
docker build -t devbox-test .
docker run -it devbox-test

---------

Co-authored-by: John Lago <[email protected]>

Author: iocron

internal/impl/generate/tmpl/devcontainerDockerfile.tmpl

@@ -4,11 +4,15 @@
 
 # Installing your devbox project
 WORKDIR /code
+{{- if not .RootUser }}
+USER ${DEVBOX_USER}:${DEVBOX_USER}
+COPY --chown=${DEVBOX_USER}:${DEVBOX_USER} devbox.json devbox.json
+COPY --chown=${DEVBOX_USER}:${DEVBOX_USER} devbox.lock devbox.lock
+{{- else}}
 COPY devbox.json devbox.json
 COPY devbox.lock devbox.lock
-{{- if not .RootUser }}
-RUN sudo chown -R "${DEVBOX_USER}:${DEVBOX_USER}" /code
 {{- end}}
+
 {{if len .LocalFlakeDirs}}
 # Step 6: Copying local flakes directories
 {{- end}}