Add form to change organization URL

What does this MR do and why?

Related to #419076 (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 sets up the Change organization URL section in Settings -> General -> Advanced. It is currently using a mock API request until GraphQL mutation for updating organization (#419608 - closed) is complete so it will not actually update the organization URL. When the API is available we will swap it in. Note there are other parts of Organizations that are still using mock data so not everything will work as expected.

Switching from mock GraphQL mutation to real one is tracked in Change organization URL form - swap mock GraphQ... (#431937 - closed)

UX notes

1. The designs in #419076 (closed) were based off the change group url form but that has since changed. I based this MR off the new styling. See screenshot below for context

2. Error message about URL not being available will be added when completing Change organization URL form - swap mock GraphQ... (#431937 - closed)

Screenshots or screen recordings

When URL has not been changed

Button disabled

When URL has been changed

Success

General error

Inline errors

How to set up and validate locally

1. Open the rails console
   • bin/rails console
2. Enable the :ui_for_organizations feature flag
   • Feature.enable(:ui_for_organizations)
3. Navigate to /-/organizations/default/settings/general and open the Advanced section

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.