Add `ng-doc-portal` dependency to `ng-doc-portal-plugin` generator so you only manually install 1 package

[zjkipping]

This would bring our plugin/generator more in-line with how other third party nx plugins deal with pulling in their dependencies for the type of project you are generating in the workspace.

Should be fairly straightforward to modify the package.json in the generator and do a package install with the Nx devkit tooling.