Transition from KEB API to KIM Runtime CR

[a-thaler]

Description

KMC is currently relying on KEB as a dependency to retrieve the list of billable clusters, see also the arch diagram.

Hereby, a REST API gets used which was not designed for that scenario and is cumbersome to use. It requires custom paging logic and complicated filtering.

Instead of relying on KEB as the source of truth on if a cluster should be billed effectively, the new infrastructure manager (KIM) with its Runtime CRD should be used. The API can be easily watched by the native kube client of the KMC controller and newly added or removed clusters can be easily observed.

Also that change will be an enabler for #90

Goal: Adjust the KMC logic to not rely on the KEB API anymore, but instead use the Runtime API of KIM.

Criterias

• There is no dependency to KEB anymore (updated arch diagram)
• RBAC settings have new read permissions for Runtime CR
• The cluster discovery logic is based on Runtime resources
• It is aligned on what criterias to watch for billing

Remarks
The current status of a Runtime CR reflects the gardener shoot status mainly, which will not be sufficient to decide on the "to bill or not to bill" decision.

The decision when to start billing should be:

• The user requested a cluster -> Runtime CR exists
• The cluster is ready to use / user can access it -> Runtime CR state was "ready" once

The decision when to stop billing should be:

• The user requested to delete the cluster -> Runtime CR is requested to be deleted

In best case, KIM will document in the CR when the cluster was ready for the first time and when it was requested to be deleted, maybe in additional status attributes, like:

• provisioned_at
• deletion_requested_at

That attributes will be also helpful later on when deciding to do a final deletion after a hibernation grace period.

[github-actions]

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