Couple k8s resource lifespan to pipelines

[k15r]

Description

In the current implementation of the manager all resources related to gateways are created on demand with the creation of pipelines.
The lifetime of these resources is not only connected to the existence of the pipeline but on their 'reconcilability'.
To simplify the code of our reconcilers we should bind the lifecycle of those resources to the lifecycle of the pipelines.

Details

• use the owner reference mechanism to automatically delete all gateway resources when the last pipeline has been deleted
• introduce a NOP pipeline-configuration for the case that (metric|trace|log)-pipelines exist, but none of them can be converted into a proper Otel configuration