Ability to override default front page route.

[Decipher]

Is your feature request related to a problem? Please describe.
As a user I want to manually set the front page route in my nuxt.config.js so I can have different front pages per frontend.

Describe the solution you'd like

• Add 'frontpage' option to the DruxtRouter module options.

  export default {
    druxt: {
      baseUrl: 'https://demo-api.druxtjs.org',
      router: {
        frontpage: '/node/1'
      }
    }
  }

  • frontpage: '/path/alias'

Describe alternatives you've considered

• You can already create a pages/index.vue and render anything you want, including <DruxtRouter path="/node/1" />

Additional context
N/A