docs: address review feedback on CONTRIBUTING.md code guidelines

- Move Code Comments section under Code Guidelines
- Remove 'Other notes on code organization' (merged into File Names)
- Remove Linter Rules subsection (duplicates other sections)
- Add Request suffix as alternative for request body types
- Remove Edit from method naming (SDK should be consistent with Update)
- Fix Enterprise/Org scoped methods description (scope from service type)
- Correct omitzero behavior for slices vs structs
- Add response body JSON tag guidance
- Mention custom pagination for non-standard APIs
- Add opts to common variable names
- Add value parameters guidance
- Use tabs in Go code examples
- Remove excessive bold formatting

Author: jlaportebot