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• [ ] update outdated documentation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 (https://github.com/kyma-project/kyma/issues/18555) than the need to expand it would become even more urgent.

[kwiatekus]

Depends on kyma-project/docker-registry#19