[Stem] Expanding the scope of Vike Extensions

[brillout]

With @nitedani we were thinking of having zero-config integrations for servers (vike-express, vike-hono, ...).

I think we can (and should!) also integrate Universal Middlewares into these server integrations.

import express from 'express'
import vike from 'vike-express'
const app = express()

// Integrates not only Vike's renderPage() but also the server endpoint of
// Telefunc/tRPC/GraphQL/...
app.use(vike)

In other words:

• Vike extensions are full-stack integrations (not only frontend)
• Vike extensions are Stem. There won't be any npm package nor GitHub repositories called "Stem".

Vike Core => only Frontend
Vike Extensions => full-stack zero-config ejectable integrations