feat!: appType (spa, mpa, custom), boolean middlewareMode (#8452)

Co-authored-by: Ben McCann <322311+benmccann@users.noreply.github.com>
Co-authored-by: Shinigami <chrissi92@hotmail.de>
Co-authored-by: Bjorn Lu <bjornlu.dev@gmail.com>

playground/ssr-vue/server.js

@@ -37,7 +37,7 @@ export async function createServer(
       root,
       logLevel: isTest ? 'error' : 'info',
       server: {
-        middlewareMode: 'ssr',
+        middlewareMode: true,
         watch: {
           // During tests we edit the files too fast and sometimes chokidar
           // misses change events, so enforce polling for consistency
@@ -47,7 +47,8 @@ export async function createServer(
         hmr: {
           port: hmrPort
         }
-      }
+      },
+      appType: 'custom'
     })
     // use vite's connect instance as middleware
     app.use(vite.middlewares)