fix: support mulltiple subnet when creating private endpoints

[andyzhangx]

What type of PR is this?

/kind bug

What this PR does / why we need it:

fix: support mulltiple subnet when creating private endpoints
when specifying "networkEndpointType: privateEndpoint" in storage class, only first subnet is associated with a new private endpoint, this does not work when there are multiple subnets. Ideally when there are multiple subnets, multiple private endpoints should be created, every private endpoint is associated with one subnet, and only one dns zone will be created mapping to vnet and multiple private endpoints
For example, in csi logs below, there are two subnets(aks-subnet, subnet2), two private endpoint(f0240127bc91d4905903342-pvtendpoint-0, f0240127bc91d4905903342-pvtendpoint-1) will be created and one private DNS zone group(f0240127bc91d4905903342-dnszonegroup) will be created.
cloud-provider-azure pr: kubernetes-sigs/cloud-provider-azure#6783
csi logs:

I0809 10:44:20.264799       1 utils.go:101] GRPC call: /csi.v1.Controller/CreateVolume
I0809 10:44:20.264829       1 utils.go:102] GRPC request: {"capacity_range":{"required_bytes":107374182400},"name":"pvc-a449228d-7696-48a9-b082-a98530a9401d","parameters":{"csi.storage.k8s.io/pv/name":"pvc-a449228d-7696-48a9-b082-a98530a9401d","csi.storage.k8s.io/pvc/name":"pvc-azurefile","csi.storage.k8s.io/pvc/namespace":"default","networkEndpointType":"privateEndpoint","skuName":"Premium_LRS","subnetName":"aks-subnet,subnet2"},"volume_capabilities":[{"AccessType":{"Mount":{"mount_flags":["dir_mode=0777","file_mode=0777","mfsymlinks","cache=strict","nosharesock","actimeo=30","nobrl"]}},"access_mode":{"mode":5}}]}
I0809 10:44:20.508800       1 azure_storageaccount.go:344] found a matching account f0240127bc91d4905903342 type Premium_LRS location eastus
I0809 10:44:21.135082       1 azure_storageaccount.go:609] Creating private endpoint(f0240127bc91d4905903342-pvtendpoint) for account (f0240127bc91d4905903342)
I0809 10:44:21.707160       1 azure_storageaccount.go:670] begin to create private endpoint(f0240127bc91d4905903342-pvtendpoint-0) on subnet(aks-subnet) under vnet(aks-vnet-27574481) in rg(MC_aks-yxytest_group_aks-yxytest_eastus)
I0809 10:44:27.370234       1 azure_storageaccount.go:670] begin to create private endpoint(f0240127bc91d4905903342-pvtendpoint-1) on subnet(subnet2) under vnet(aks-vnet-27574481) in rg(MC_aks-yxytest_group_aks-yxytest_eastus)
I0809 10:44:33.498485       1 azure_storageaccount.go:721] Creating private DNS zone group(f0240127bc91d4905903342-dnszonegroup) with privateEndpoint(f0240127bc91d4905903342-pvtendpoint-0), vNetName(aks-vnet-27574481), resourceGroup(MC_aks-yxytest_group_aks-yxytest_eastus)
I0809 10:44:34.687096       1 azure_storageaccount.go:721] Creating private DNS zone group(f0240127bc91d4905903342-dnszonegroup) with privateEndpoint(f0240127bc91d4905903342-pvtendpoint-1), vNetName(aks-vnet-27574481), resourceGroup(MC_aks-yxytest_group_aks-yxytest_eastus)
I0809 10:44:35.663168       1 controllerserver.go:568] begin to create file share(pvc-a449228d-7696-48a9-b082-a98530a9401d) on account(f0240127bc91d4905903342) type(Premium_LRS) subID() rg(MC_aks-yxytest_group_aks-yxytest_eastus) location() size(100) protocol(SMB)
I0809 10:44:35.925792       1 controllerserver.go:600] create file share pvc-a449228d-7696-48a9-b082-a98530a9401d on storage account f0240127bc91d4905903342 successfully
I0809 10:44:35.935106       1 controllerserver.go:646] store account key to k8s secret(azure-storage-account-f0240127bc91d4905903342-secret) in default namespace
I0809 10:44:35.935406       1 azure_metrics.go:118] "Observed Request Latency" latency_seconds=15.670012553 request="azurefile_csi_driver_controller_create_volume" resource_group="mc_aks-yxytest_group_aks-yxytest_eastus" subscription_id="" source="file.csi.azure.com" volumeid="MC_aks-yxytest_group_aks-yxytest_eastus#f0240127bc91d4905903342#pvc-a449228d-7696-48a9-b082-a98530a9401d###default" result_code="succeeded"
I0809 10:44:35.935528       1 utils.go:108] GRPC response: {"volume":{"capacity_bytes":107374182400,"volume_context":{"csi.storage.k8s.io/pv/name":"pvc-a449228d-7696-48a9-b082-a98530a9401d","csi.storage.k8s.io/pvc/name":"pvc-azurefile","csi.storage.k8s.io/pvc/namespace":"default","networkEndpointType":"privateEndpoint","secretnamespace":"default","server":"f0240127bc91d4905903342.privatelink.file.core.windows.net","skuName":"Premium_LRS","subnetName":"aks-subnet,subnet2"},"volume_id":"MC_aks-yxytest_group_aks-yxytest_eastus#f0240127bc91d4905903342#pvc-a449228d-7696-48a9-b082-a98530a9401d###default"}}

Which issue(s) this PR fixes:

Fixes ##2047

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Special notes for your reviewer:

Release note:

none

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: andyzhangx

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[andyzhangx]

/retest

[k8s-ci-robot]

@andyzhangx: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-azurefile-csi-driver-e2e-capz-windows-2019	52cf419	link	true	/test pull-azurefile-csi-driver-e2e-capz-windows-2019

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[andyzhangx]

/retest