CLI chaining support for install and build

You can already chain e.g. ``flask webpack create install`` like this, but you cannot chain other commands after install or build, e.g. you can't ``flask webpack create install build``.

This is because we accept arbitrary options after install which is passed to NPM.

Would be nice if there was a way to allow ``flask webpack create install build``

Start by locating the CLI handling for install and build, then inspect how arbitrary options after install are forwarded to NPM. Done means commands can be chained after both install and build, including `flask webpack create install build`, without breaking supported NPM options.

Written by the indexing model from the issue text.