[FEATURE] Add option to include custom template

[chaoticbear]

Proposal

The current plop generator is a great workflow tool, and has some good standard files included with the template.

In some cases a group's workflow may want to include other files as part of the generation. For example in our case we wanted to add a component-name.props.ts file with a basic scaffold of props for a component.

To support that option I've added an option to add a custom template file for example component-name.props.ts

Usage

By default the templates are unchanged from the original set, and the config is not required to exist.

The steps for a new template file include:

1. Add a new template file to your local project. eg. props.hbs
2. Add the template as an additional template in the plopfile atomicGenerator config:

additionalTemplates: [
  {
    extension: 'props.ts',
    template: 'generators/atomic-component/templates/props.hbs',
  },
],

[chaoticbear]

@ahoendgen Let me know if you need anything else with this PR.