Update yarn start command and doc for worker

[FelixMalfait]

As we deprecate the sync driver for worker we need to update the documentation and make it seemless for people to start the worker in a development environment (including adding it to yarn start)

[BOHEUS]

Is it still valid? @martmull added worker to npx nx start in #7820

[martmull]

Maybe we could check if doc is up to date but worker starts when now nx start is launched

[BOHEUS]

I checked docs and there's no mention about sync driver in environmental variables, also checked pages in Backend development, no mention too but won't hurt if someone else also re-check

[FelixMalfait]

All good now, thanks! Closing