Add gallery to the About section

[fhlavac]

Enhance the "About component groups" page with a gallery view similar to the "Extensions" section: https://staging-v6.patternfly.org/extensions/about-extensions/

@edonehoo and @fhlavac to find a way of displaying all components but also mention their category

RHCLOUD-35173

[nicolethoen]

I believe this landing page can be built following the model for building out a gallery/about page for the extensions. That code for the extensions about page lives at https://github.com/patternfly/patternfly-org/tree/main/packages/documentation-site/patternfly-docs/pages/landing-pages/extensions.

Build out a data file to list all the component groups + summaries of their purpose, then use the SectionGallery component from @patternfly/documentation-framework.

The patternfly-docs.source.js file might need to be updated to know to look for this new about page as well.

[fhlavac]

@nicolethoen awesome, thanks for all the information!