Allow configuration for internal docker registry volume

[kwiatekus]

Description

Expose internal docker registry storage size in the serverless CR:

  spec:
    dockerRegistry:
      enableInternal: true
      size: 20Gi

• when edited in the DockerRegistry CR the operator should reconfigure the PVC
• operator should execute a rollout restart of the docker registry workload in order to allow volume expansion
• provide documentation about this configurability option
• update outdated documentation
• when actual PVC size is different from desired (default=20Gi) than DockerRegistry CR should result in warning condition
• actual used size is shown in the status

Reasons

At the moment it it a fixed value of 20 Gi and for some users who use serverless extensively it is not enough.
Additionally, if we expose it for other usecases as well (kyma-project/kyma#18555) than the need to expand it would become even more urgent.

[kwiatekus]

Depends on #19

[kwiatekus]

Docker registry comes now with the option to configure pvc or allows setting alternative HA storage variants like s3 bucket, azure storage ,gcs or SAP BTP Object Store.
Managing the volume size of the default PV seems redundant, and also introduces lifecycle management problems related with resizing of already mounted volumes.
Closing as wontfix