[chore] remove obsolete note about auth type limitations in `k8sclust…

…erreceiver` (#35853)

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Ex. Adding a feature - Explain what this achieves.-->
#### Description

This PR removes the note about `serviceAccount` being the only auth type
being supported by the `k8sclusterreceiver`, since in the meantime
support for `kubeConfig` auth type has been added (also verified this
manually to be safe)

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#### Documentation

Updated the readme of the `k8sclusterreceiver`

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Signed-off-by: Florian Bacher <[email protected]>

receiver/k8sclusterreceiver/README.md

@@ -19,9 +19,6 @@ The Kubernetes Cluster receiver collects cluster-level metrics and entity events
 API server. It uses the K8s API to listen for updates. A single instance of this
 receiver should be used to monitor a cluster.
 
-Currently, this receiver supports authentication via service accounts only. See [example](#example)
-for more information.
-
 ## Metrics
 
 Details about the metrics produced by this receiver can be found in [metadata.yaml](./metadata.yaml) and [documentation.md](./documentation.md).