Allow specifying custom Detectors in `otelcol.processor.resourcedetection` Block

[SeamusGrafana]

Allow specifying custom detectors (such as gcp) in the otelcol.processor.resourcedetection block.

https://grafana.com/docs/alloy/latest/reference/components/otelcol.processor.resourcedetection/#arguments

For example if you have a K8s Cluster on GCP or AWS etc, you may want to enrich your data with the attributes provided from here.

If you can specify additional values, you would be able to do this.

[cyrille-leclerc]

As the OTLP Alloy instances are not Kubernetes DaemonSets deployed on each Kubernetes node, we think that the ResourceDetection processor is likely to produce erroneous attributes. typically, host.name, host.id, or host.ip are likely to be erroneous.
Attributes like cloud.availability_zone, cloud.region, or k8s.cluster.name are less likely to be erroneous.