[documentation] update config.river sample for k8s ebpf use case

[yashsarma]

Error: /etc/agent/config.river:61:47: field "targets" does not exist

60 |     forward_to = [pyroscope.write.endpoint.receiver]
61 |     targets = discovery.relabel.specific_pods.targets
   |                                               ^^^^^^^
62 | }

ts=2024-03-21T16:17:33.064918553Z level=error msg="failed to start reporter" err="context canceled"
interrupt received
Error: could not perform the initial load successfully

[CLAassistant]

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1 out of 2 committers have signed the CLA.

✅ simonswine
❌ yashsarma
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[knylander-grafana]

Thank you for submitting a fix for the docs! I'm going to defer to someone who can verify your update to approve.

[simonswine]

LGTM

Thank you @yashsarma for spotting the problem and fixing it. You just need to sign the CLA in order for us to merge the PR.

While testing your change I also noticed another problem, which I fixed in the same go.