Create 'ng add' schematic

[benjamincharity]

https://angular.io/guide/schematics-for-libraries

We should provide a simple schematic so that ng add @terminus/ui works as expected by consumers. This will also act as the proof of concept for more complex schematics (such as breaking change migrations)

At the very least this action should:

1. Install the UI library
2. Install all needed dependencies
3. If possible, include a prompt asking if the optional dependencies should be installed

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• https://angular.io/guide/creating-libraries
• https://angular.io/guide/schematics-for-libraries
• https://nitayneeman.com/posts/making-an-addable-angular-package-using-schematics/