Docs: Improve documentation of the grid

[xak]

The grid documentation is not very useful.

https://sap.github.io/fundamental/foundation/grid.html

Detailed description

• The grid specs are not up-to-date with the Fiori 3.0 recommendations
• The breakpoints have changed

Reference

See specs

[xak]

@LeoT7508 This is high priority. The previous images — https://github.com/SAP/fundamental/tree/develop/docs/images/grid — are no longer valid with the new specs from #747

[saad-mo]

@LeoT7508 any update on this?