Add k8s cluster fields for private node pools feature

[avorima]

Current SDK Version

v6.1.7

Use-cases

The SDK needs to support the upcoming private node pools feature to allow tools like ionosctl or terraform to create private node pools.

Proposal

The cloud API accepts the following new k8s cluster fields:

• location: string
• natGatewayIp: string
• nodeSubnet: string
• public: boolean

References

https://api.ionos.com/docs/cloud/v6/#tag/Kubernetes/operation/k8sPost

[cristiGuranIonos]

Done in https://github.com/ionos-cloud/sdk-go/releases/tag/v6.1.11