Setup new group from organization route, controller, and Vue app

What does this MR do and why?

Related to #410804 (closed)

The grouptenant scale team is starting to build out an Organization MVC. For more information about what an "Organization" will be see https://docs.gitlab.com/ee/architecture/blueprints/organization/

This MR is the start of adding a form to create a new group in an organization. To help keep MRs on the smaller side this feature will be split up into multiple MRs. This MR does the following:

1. Sets up route and controller
2. Sets up basic Vue app with page title and description

Future MRs will:

1. Build new group form
2. Add New group button that links to this page will be added to the Groups and projects page in !142346 (merged)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

How to set up and validate locally

1. Open Rails console
   • bin/rails console
2. Enable the feature flag
   • Feature.enable(:ui_for_organizations)
3. Navigate to /-/organizations/default/groups/new