Remove every reference to .nuxt global option

[cnotv]

Description

Remove or replace with documentation self-declarative naming .nuxt global options, configurations, and related use cases:

• $nuxt
• $options.nuxt.error
• Entry definitions with .nuxt object
• Rehydrate function (should not be in use) https://github.com/rancher/dashboard/blob/master/shell/plugins/dashboard-store/rehydrate-all.js#L6
• All the generated folder references, e.g. ignoring .nuxt

Context

Most of the configurations leftovers from Nuxt are about global properties used just within it, so probably unused everywhere else or deprecated. It's a layer of complexity that is unnecessary and unknown to us.