Microfrontends example: Missing package version blocks the app build

[kkomelin]

The project can't be build or start because the apps in the apps folder lack necessary dependencies, which are not installed on yarn install because of some missing package data.

yarn create next-app --example https://github.com/vercel/examples/tree/main/solutions/microfrontends microfrontends

> yarn install

yarn install v1.22.18
warning Missing version in workspace at "/srv/apps/my/microfrontends/apps/docs", ignoring.
warning Missing version in workspace at "/srv/apps/my/microfrontends/apps/main", ignoring.

> yarn build

docs:build: $ next build
main:build: $ next build
docs:build: /bin/sh: 1: next: not found
main:build: /bin/sh: 1: next: not found
docs:build: error Command failed with exit code 127.
docs:build: info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
main:build: error Command failed with exit code 127.
main:build: info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
main:build: ERROR: command finished with error: command (apps/main) yarn run build exited (127)
command (apps/main) yarn run build exited (127)

PR provided #363