dx: windows: Improve setup instructions

- `npm ci` instead of `npm install` (much faster on windows cmd)
- node script for submodule rather than bash script (so not to as require git bash)
- installing packages for frontend, plugins, and making backend could be done in parallel
- Could there be one command to install?
- (maybe optional) Having to download and install az on a slow network connection is very slow (2mbit connection isn't even really "slow")... if can use existing az install that would be much quicker to get started. Maybe a separate command to use already installed az, and only download it if it's not there.