Can't run `npm run quickstart` on main branch -> lerna bootstrap was removed in v7

## Description
Running `npm run quickstart` in a new environment, yields the following error
```console
ERR! bootstrap The "bootstrap" command was removed by default in v7, and is no longer maintained.
ERR! bootstrap Learn more about this change at https://lerna.js.org/docs/legacy-package-management
```

## Reproduce

1. run `npm run quickstart`

## Expected behavior

Build the repo.

## Context

- JupyterLite version: 0.2.0a1 ?
- Operating System and version: ArchLinux
- Browser and version: irrelevant