OWNCLOUD_SUB_URL not supported

[Jishun]

OWNCLOUD_SUB_URL is needed when deployed through a a reverse proxy under a child path, such as in k8s ingress

I was deploying it to http://localhost/owncloud/ but it assumes itself at / and will redirect to the invalid path
tried to add OWNCLOUD_SUB_URL value to the k8s yaml config and it didn't fix the issue as it should
mentioned here
owncloud-docker/base#38