Rewrite schema build page

Description of feature

The pipeline launch page is one of the few that didn't make it into the new Astro rebuild. At the time of writing, that's still running at https://oldsite.nf-co.re/pipeline_schema_builder with source code lurking on the old-site branch here. We do some redirection magic to make that new website render the URL from the oldsite without anyone knowing 🤫

We need to rewrite the nf-core schema build pages. This should be removed from the website entirely and instead be integrated into the nf-core CLI - it's for developers only so has no real benefit from being part of the website, and it's nicer to keep things offline if possible. We should be able to run a local server quite easily with http.server or similar to give a very similar experience to what we have currently.