Enable using PV as model cache directory

[yongfengdu]

Set modelUsePV to pvc name for model cache

Description

modelUsePV support

Issues

#128

Type of change

List the type of change like below. Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would break existing design and interface)

Dependencies

List the newly introduced 3rd party dependency if exists.

Tests

Verified using nfs as PV backend.
Setup example:
PV:
apiVersion: v1
kind: PersistentVolume
metadata:
name: nfspv
spec:
capacity:
storage: 300Gi
volumeMode: Filesystem
accessModes:
- ReadWriteMany
persistentVolumeReclaimPolicy: Retain
storageClassName: nfs
nfs:
path: "/data/nfspv"
server: "192.168.0.184"
readOnly: false

PV Claim:
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
name: model-volume
spec:
accessModes:
- ReadWriteMany
storageClassName: "nfs"
resources:
requests:
storage: 1Mi

Test example with whisper:
helm install whisper whisper --set global.modelUseHostPath="" --set global.modelUsePV=model-volume --set replicaCount=4 --set image.tag=latest

[lianhao]

We need to add a common README of how to use and configure PV to be used. But that could be done in another PR, since we need to figure out where to put it

[daisy-ycguo]

lgtm