Is your feature request related to a problem? Please describe.
Currently I can either change root to a subfolder (which doesn't work for all other folders outside) or have root at the root but it needs an index.html in this directory.

Something like a monorepo where I have a /fixture or /playground folder for development but it should also watch all other packages in /packages/. Setting root to /playground works but doesn't include all other files outside.

I know monorepo support is currently a future thing but don't know if it's really a monorepo "problem". Is this even possible or does the root need to be always where the index.html is?

Describe the solution you'd like
Maybe introducing a new option entry/indexEntry to be able to change the location e.g. --entry=./playground/index.html or from the vite.config.ts.

Additional context
Current project structure:

Root
├── packages     <-- but should also watch those
│   ├── package-1
│   └── package-2
└── playground   <-- this is the "dev" environment
     ├── index.html
     ├── App.vue
     └── main.ts