Export resource usage statistics

[a-thaler]

Description

If cluster usage can be collected and exported successfully, but still the data does not arrive in the target system because of problems out of control of KMC, it is very helpful to see what data got tracked. Also, making the data introspectable will help troubleshooting.

Goal: Provide transparency on billed items by exporting the technical usage data as operational metrics

Criterias:

• For every resource usage being collected, a corresponding gauge metric gets exported
• Metric is labeled with the action and optional resource type (machine type, redis tier,..)
• Naming is consistent to changes done here: Migrate to otel_sdk instead of prometheus_client #121

Metrics proposal:

• kmc_collected_machine_instances{type="n2_standard4", shoot="123", globalaccount_id,="xxx" subaccount_id="xxx", instance_id="xxx"} 5
• kmc_collected_volume_bytes{type="default", shoot="123",globalaccount_id,="xxx" subaccount_id="xxx", instance_id="xxx"} 582378
• kmc_collected_volumebackups_bytes{type="default", shoot="123",globalaccount_id,="xxx" subaccount_id="xxx", instance_id="xxx"} 43434545
• kmc_collected_cloudmanager_nfs_bytes{type="default", shoot="123",globalaccount_id,="xxx" subaccount_id="xxx", instance_id="xxx"} 44356
• kmc_collected_cloudmanager_redis_instances{type="S1", shoot="123",globalaccount_id,="xxx" subaccount_id="xxx", instance_id="xxx"} 2