Create a client.

This endpoint is only available to API clients with admin access. Admin access allows an API client to
manage other API clients through the /clients endpoints. Admin access is not enabled by default and
must be explicitly granted by CM.com. It cannot be requested or changed through the API.

There is no dedicated endpoint to check your admin access in advance: calling this endpoint without admin
access returns 403 Forbidden, while a successful call confirms you have admin access.