feat: add 3 new variants for display group: box_gray, box_primary, box_secondary

[jfmcquade]

PR Checklist

• [x] PR title descriptive (can be used in release notes)

Description

Adds 3 new variants for the display_group component: box_gray, box_primary and box_secondary.

Whilst there is considerable refactoring that could be done to improve the display group code, these visual variants (a grey box at least) are required for an imminent release, so the general improvements to the code are minimal.

Git Issues

Closes #2149

Screenshots/Videos

Updates to feature_display_group

[chrismclarke]

Should be allow both gray and grey? In general I think we've favoured UK spelling

haha, was exactly my question! the difference gives soo much grief from a dev perspective, I think consensus is generally for code you should be using american version (like we do for things like color and center), but given we also want to support authors likely best to have both. Similar discussion from a while back on tailwind style library: https://github.com/tailwindlabs/tailwindcss/issues/521

[esmeetewinkel]

(like we do for things like color and center),

Interesting you say that, the header PR that's happening in parallel uses colour (or does it allow both?)

[chrismclarke]

Interesting you say that, the header PR that's happening in parallel uses colour (or does it allow both?)

No for that one we'll be converting from colour in the config to color in the code, so yeah might be a bit confusing for anyone that uses US-English. Might also be good to support both (ideally by converting in the parser instead of explicitly handling in the code)