Replace dt in AppMosaic to make it more versatile and accessible

[eddybrando]

In the AppMosaic component, we are currently using description lists (<dl>), which made total sense for its initial usage in the home page, but could restrict the reusability of this component in other scenarios.

Since we recently refactored the component in order to reuse it, it may be a good time to think about this.

If we were to pass to the AppMosaic a list of mosaicElements which are not name-value groups, we wouldn't be using the description list correctly (spec: https://html.spec.whatwg.org/multipage/grouping-content.html#the-dl-element).

This could be particularly problematic for screen readers, which may hint the user about a text inside a <dd> tag being the description of a text inside a <dt> tag, which wouldn't be always the case.