[docs][examples] Update k8s example to not use 0.0.0.0 on OTLP receiver endpoint

[mx-psi]

We raise a warning when using the default OTLP receiver endpoints to mitigate DoS attacks.

Our Kubernetes based example however, uses the default endpoints:

opentelemetry-collector/examples/k8s/otel-config.yaml

Lines 11 to 15 in 9257d7f

	receivers:
	otlp:
	protocols:
	grpc:
	http:

We should follow the approach that was done in the Helm chart (see open-telemetry/opentelemetry-helm-charts/pull/603) to pass the pod IP through an environment variable.

Once that example is updated, we should link it on the security best practices page as an example of what to do on containerized setups, to avoid the confusion brought up in both #7488 and #6938.