feat: downgrade SSR to SPA, when node server crashes

[falstack]

What problem does this feature solve?

when Node server is crashed, Nginx will send error page to client, i want custom the error page and use index.spa.html, how should i do?

What does the proposed changes look like?

when Node server crashed, Nginx send Project/.nuxt/dist/server/index.spa.html to client

_{This feature request is available on Nuxt community (#c8206)}