Add new "highlights" container layout

[cemms1]

Co-authored-by: Wai Sing Yiu [email protected] Co-authored-by: Frederick O'Brien [email protected]

What's changed?

Adds new container layout for use as the "highlights" container.

This is a new container layout intended to only be used once per front, in the first position only. This is intended to be guided by training and not enforcement in the tool.

If the first container on a front has this highlights layout, it will be positioned above the title piece/nav sections on both web and apps to showcase feature stories across the site.

The display on desktop is to show three content items and a "peek" of the fourth item. On mobile and apps it will display two content items and a "peek" of the third item.

Implementation notes

Checklist

General

• [ ] 🤖 Relevant tests added
• [ ] ✅ CI checks / tests run locally
• [ ] 🔍 Checked on CODE

Client

• [ ] 🚫 No obvious console errors on the client (i.e. React dev mode errors)
• [ ] 🎛️ No regressions with existing user interactions (i.e. all existing buttons, inputs etc. work)
• [ ] 📷 Screenshots / GIFs of relevant UI changes included