fix setup steps for apps build including rosetta

[davidsbailey]

This PR addresses two setup issues:

1. configure all developers to build and use local apps package, to address a general setup issue that most developers have to go back and fix later
2. fix apps build failure on M-series mac in case where Rosetta has not already been installed. see slack for error details.

I'm including step (1) as a fix for an issue I ran into where I followed all the setup steps but then could not load http://localhost-studio.code.org:3000 due to missing js assets. While it may appear that there is support for developers to run without a local apps build, this does not work reliably in practice outside of chef-managed environments since it relies on an apps package having already been built by the staging or test machine, which is not generally true after a developer pulls latest staging. Based on that it seems reasonable to always generate and use the local build. For more details, search the code for build_apps and use_my_apps.