feat: M2M access keys

[dokterbob]

Allow creating and/or retrieving M2M access keys.

https://docs.descope.com/m2m-access-keys
https://docs.descope.com/api/management/access-keys/create-access-key

This greatly increases the utility of Terraform provider as it allows automatic provisioning of credentials for integrating applications.

[shilgapira]

We're considering expanding the scope of the Terraform provider to manage additional entities but I don't have a concrete timetable yet. I'll post here when I have an update.