Add StirStudios/stir_nuxt_base as nuxt demo starter

Let's add https://github.com/StirStudios/stir_nuxt_base as another demo-starter!

Proposed resolution

Make a gitpod URL that uses a different frontend-repo and add it to https://github.com/drunomics/lupus-decoupled-website
Is it a layer or a full repo now? If a layer, I guess we could just add a small wrapper demo-repo to make it work witih gitpod? I'm opening a dedicated sub-issue for it!