L3 grid system

[pahupe]

Goals:

• Implement a 12-column based grid system with fixed margins (left/right), fixed gutter space (space between columns) where the elements (e.g. cards) that span 1..n columns stretch
• For 1600px+ width, implement a grid system where the margins enlarge, but neither the columns nor gutter resize

Basically, this creates a grid as on the existing pages (https://news.sap.com/tags/ai/) with "stretching" elements

References:

• https://sap.frontify.com/document/223141#/layout/grid-breakpoints
• https://adobe-dx-support.slack.com/archives/C06H8UNQ3RS/p1707727508931139

[benpeter]

@saurabh-khare -- please focus on L3 for now, other levels later + split to separate issues (happy for you to create these)