Improve the Gallery in the About page

[fhlavac]

A follow-up to #366

RHCLOUD-35699

In the next phase, we have a gallery for each category and within the gallery, the cards are the individual component groups

We need to enhance the SectionGallery to support that

The code lives here:
https://github.com/patternfly/patternfly-org/blob/main/packages/documentation-framework/components/sectionGallery/sectionGallery.js

at the same time, it would be nice to add a prop hiding the filter if there is just a few components in the category

[andrew-ronaldson]

Made a design issue for this. We can try to tackle this in Q1 if there is time.