I have one yaml file that contains the following:

...
volumeMounts:
      - mountPath: /var/lib/grafana
        name: grafana-storage
      - mountPath: /etc/grafana/provisioning/datasources
        name: grafana-datasources
        readOnly: false
...

and another file in witch the grafana-datasource volume is specified:

apiVersion: v1
kind: ConfigMap
metadata:
    name: grafana-datasources
    namespace: ccx-data-pipeline
    labels:
        grafana_datasource: '1'
data:
    prometheus.yaml: |-
        {
            "apiVersion": 1,
            "datasources": [
                {
                    "access":"proxy",
                    "editable": true,
                    "name": "prometheus-ccx-service",
                    "orgId": 1,
                    "type": "prometheus",
                    "url": "http://prometheus-service:9090",
                    "version": 1
                }
            ]
        }

the point is that

"url": "http://prometheus-service:9090" 

can't be hard coded but must be parametrized (ideally with an environment variable). It would be great to do like so:

"url": "${ENDPOINT}"

but it doesn't work, probably due to the |- syntax. Is there an elegant way to achieve this?