kit advanced layout

[indaco]

This PR brings the following changes:

Fixed Bug:

• api endpoints were still on old sveltekit routing mechanism. Updated and fixed an issue when building the project due to prerender=true on those files. fallback: '200.html' on static adapter configuration made the magic.

Features:

• new resource cmd allows to specify the group layout name according to the sveltekit Advanced layouts by passing the --group flag

   sveltin new resource testimonials --group marketing

• new resource cmd allow to specify if a different layout for the slug pages must be created in addition to the one for the index page.

   sveltin new resource posts --slug

Chores:

• sveltekit updated to next.483
• go deps updated
• uniform function names

Refactor:

• config.TemplateData struct makes use of individual struct for each artifact template data
• file templates updated accordingly
• generate commands (menu, rss, sitemap) simplified and updated to work for grouped layout too