fix(create-hops-app): force legacy peer deps handling for npm@7
fix(create-hops-app): force legacy peer deps handling for npm@7

npm@7 introduced new behaviour for peer dependencies and installs them
automatically.
Unfortunately this breaks our integration tests because
react-helmet-async does not yet support react@17.
With this commit we add a CLI flag for the npm install command to force
npm to switch back to the previous behaviour to not automatically
install peer dependencies.
We can remove this again once react-helmet-async support react@17.

xing/hops,xing/hops,xing/hops