Document rubocop manual todo file

What does this MR do?

• regenerates rubocop todo file
• follow on of !49416 (merged) to further document use of manual todo file.

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

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/280547