Add fields required to support self-managed certificates

[impl]

Description

When programmatically managing self-managed certificates, i.e. by requesting the /verify endpoint in code, the caller needs needs to know the values of the origin domain name and the cname-api-key header to set up the reverse proxy correctly. This change simply adds those two fields to the CustomDomain struct.

References

• Add support for creating external resources associated with self-managed certificates terraform-provider-auth0#118

Testing

• This change adds test coverage for new/changed/fixed functionality

Checklist

• I have read and agreed to the terms within the Auth0 Code of Conduct.
• I have read the Auth0 General Contribution Guidelines.
• I have reviewed my own code beforehand.
• I have added documentation for new/changed functionality in this PR.
• All active GitHub checks for tests, formatting, and security are passing.
• The correct base branch is being used, if not main.

[sergiught]

Thanks for the contribution @impl ! 🥳 Great addition!

We'll aim at making a release by the end of this week so we can reference the new version within the terraform provider as well.

[sergiught]

Tests will fail cuz this is coming from a fork but they pass locally:

We'll try to open these for forks as well soon, but there's some work we need to do first.