Improve ACL documentation, warn users about default values

[OpenNebulaSupport]

Description Improve documentation about managing permissions and ACLs. The current documentation does not explicitly state that various ACLs for normal users are created by default. This causes confusion among some OpenNebula users and can be a potential security risk in newly created environments.

Use case Documentation should clearly warn about default ACLs and encourage users to carefully adjust them.

Interface Changes N/A

Additional Context N/A

Progress Status

• [ ] Branch created
• [ ] Code committed to development branch
• [ ] Testing - QA
• [ ] Documentation
• [ ] Release notes - resolved issues, compatibility, known issues
• [ ] Code committed to upstream release/hotfix branches
• [ ] Documentation committed to upstream release/hotfix branches