Redesign the "Added in" badges in the docs

[mdo]

Cherry-picked from #35736. /cc @XhmikosR

[XhmikosR]

This needs to land after #35979 since that's where fw-semibold is added. Other than that, LGTM!

[WinterSilence]

extract duplicate labels <small class="d-inline-flex px-2 py-1 fw-semibold text-success bg-success bg-opacity-10 rounded-2">Added in v...</small> into /site/layouts/shortcodes/:

{{- /*
  Usage: `since version`

*/ -}}

{{- $version := .Get "version" | default $.Site.version -}}

<small class="d-inline-flex px-2 py-1 fw-semibold text-success bg-success bg-opacity-10 rounded-2">Added in v{{ $version }}</small>

[XhmikosR]

@WinterSilence thanks, but I think it'd be better if you made a PR later after this has landed.