Create Cells sections as separate files

What does this MR do and why?

Create Cells sections as separate files

This moves glossary, goals and impact into separate documents, making the main one more like a document with many links.

This allows to better structure the work.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.