Add visibility level field

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 builds on top of !142598 (merged), !143709 (merged) and !144425 (merged) to continue building out the form to add a group to an organization. This MR adds the Visibility level field to the form. This form does not actually do anything yet when submitted. See reviewer notes for changes in future MRs.

Reviewer notes

1. Future MRs will add:
   • Your group name must not contain a period if you intend to use SCIM integration, as it can lead to errors. alert that is shown on https://gitlab.com/groups/new#create-group-pane
   • Add Who will be able to see this group? View the documentation under Visibility level label. We need to add support upstream in gitlab-ui!3982 (merged) before this is possible.
   • API call that creates the group.
2. The plan is to use this new Vue form to refactor /groups/new#create-group-pane ( #440464) and /admin/groups/new ( #440466) to Vue in the future.

MR acceptance checklist

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Screenshots or screen recordings

How to set up and validate locally

1. Enable the feature flag
   • echo "Feature.enable(:ui_for_organizations)" | gdk rails c
2. Navigate to /-/organizations/default/groups_and_projects
3. Click New group