Update to docker guidence

[nikiwycherley]

Description

Updates Docker guidance to address SonarCloud security vulnerability related to file permissions in COPY commands.

Problem

SonarCloud flags COPY --chown=node:node commands with the error: "Make sure no write permissions are assigned to the copied resource." This occurs because giving the running user ownership of files grants write permissions, creating an unnecessary security risk - see https://rules.sonarsource.com/docker/type/Security%20Hotspot/RSPEC-6504/

Solution

Changed all COPY commands from --chown=node:node to --chown=root:root in Dockerfile examples. This ensures:

• Files are owned by root:root
• Container runs as non-root user (node)
• Running user has no write permissions to application files
• Satisfies security scanning requirements without additional chmod commands

Changes Made

• Added new "Security best practices" section explaining file ownership in COPY commands
• Updated multi-stage build example to use --chown=root:root in both development and production stages
• Documented why this approach is more secure than alternatives

Files Changed

• docs/guides/docker_guidance.md

Security Impact

This change improves security posture by ensuring containerized applications follow the principle of least privilege - the running user cannot modify its own application files.