ionoscloud: Update ionos-cloud-sdk-go and add metrics

[avorima]

What type of PR is this?

/kind cleanup
/kind feature

What this PR does / why we need it:

Address a few things that built up over time:

• Update ionos-cloud/sdk-go to v6.1.11
• Fix example values link in provider README
• Configurable additional request headers
• Add cloud API response metrics

# HELP cluster_autoscaler_ionoscloud_api_request_total [ALPHA] Counter of IonosCloud API requests for each action and response status.
# TYPE cluster_autoscaler_ionoscloud_api_request_total counter
cluster_autoscaler_ionoscloud_api_request_total{action="DeleteNode",status="success"} 1
cluster_autoscaler_ionoscloud_api_request_total{action="GetNodePool",status="success"} 12
cluster_autoscaler_ionoscloud_api_request_total{action="ListNodes",status="success"} 10
cluster_autoscaler_ionoscloud_api_request_total{action="ResizeNodePool",status="success"} 1

Does this PR introduce a user-facing change?

Add `cluster_autoscaler_ionoscloud_api_request_total` alpha metric

[piepmatz]

The ticket mentions "Allow deploying in-cluster autoscaler in staging". Is that reflected in here somehow? If so, where?

[piepmatz]

The PR description's metrics example looks outdated.

[avorima]

The PR description's metrics example looks outdated.

Ah, seems I forgot to push my latest changes.

[avorima]

The ticket mentions "Allow deploying in-cluster autoscaler in staging". Is that reflected in here somehow? If so, where?

The client is always constructed using config, which means that the endpoint is used even when IONOS_TOKEN is set.

[piepmatz]

LGTM