Added new and optional routing field to a regional hostname

[tarnfeld]

We're (slowly) introducing a new field into the Regional Hostnames API. It's optional and will be null/empty for most cases.
Motivation here is to get an updated schema into the Cloudflare terraform provider.

Description

Nothing complicated here, just a new field. The docs on https://developers.cloudflare.com/api will be out momentarily.

Has your change been tested?

I've left the existing tests unchanged and added some new tests that include the new field.

Types of changes

What sort of change does your code introduce/modify?

• New feature (non-breaking change which adds functionality)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.
• This change is using publicly documented in cloudflare/api-schemas
  and relies on stable APIs.