Pull API tokens from Kubernetes Secrets

[luke-clinch]

First of all, hats off for this great piece of work - we have favoured using this over SNMP for feeding metrics to Grafana Cloud. The dashboard is fab.

We have deployed the Fortigate Exporter as a pod on bare metal Kubernetes. (v1.28)
Our configmap contains the api token used by the Fortigate Exporter deployment to authenticate to our Fortigates.
To avoid storing credentials in the clear, we'd like to store the api token as a Kubernetes Secerets.
Is this supported? How should the k8s secret variable be referenced in the configmap / fortigate-key.yaml?