Make codeowners docs more clear

What does this MR do?

Makes the documentation a bit more clear for customers when trying to only use the CODEOWNER file in repo root to determine who can approve merge requests (no Merge request rules defined)

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content