网上搜到了很多，
有说用projected volumn的–不好用
有说用subpath加key的–我用也不好用

放上亲测可用的,关键点是volumeMounts的mountpath最后是直接加文件名（本来subpath是设计来避免文件夹覆盖的，这里文件也可以这么用。）

volumeMounts:
- name: cfg-vol
  mountPath: /etc/grafana/provisioning/datasources
- name: cfg-ini
  mountPath: /usr/share/grafana/conf/sample.ini
  subPath: sample.ini
- name: cfg-temp
  mountPath: /usr/share/grafana/conf/test.json
  subPath: test.json

  volumes:
  - name: cfg-vol
    configMap:
      name: cm-grafana-yaml
  - name: cfg-ini
    configMap:
      name: cm-grafana-ini
  - name: cfg-temp
    configMap:
      name: cm-grafana-temp