[Fix]: Better output when installing with NPM

Why do you want this feature?

In the postinstall.sh script that is used when installing with npm, we use nested commands to install vscode and its extensions - see code

As reported in https://github.com/coder/code-server/issues/5530 (and more in https://github.com/coder/code-server/pull/5533), installs were passing but actually failing - and only was seen during runtime.

The nested installs were failing, but the errors weren't being bubbled-up... Was only seen when using --foreground-scripts.

NPM 8 needs to be passed --foreground-scripts to actually see the output of the nested. We should update the doc to show that as a troubleshooting step in here: https://coder.com/docs/code-server/latest/npm#debugging-install-issues-with-npm
I would expect the overall script to have a non-0 exit code if any of the nested scripts failed (i.e. they themselves had a non-0 exit code) which would make the overall npm install fail. Need to investigate that.

Yes