Fix velero install example

[fxierh]

The storageAccount key passed to the velero install --backup-location-config argument should contain the storage account name, not the storage account ID.

/kind changelog-not-required

[kaovilai]

The "ID" came from the variable defined like following.

AZURE_STORAGE_ACCOUNT_ID="velero$(uuidgen | cut -d '-' -f5 | tr '[A-Z]' '[a-z]')"
az storage account create \
    --name $AZURE_STORAGE_ACCOUNT_ID \
    --resource-group $AZURE_BACKUP_RESOURCE_GROUP \
    --sku Standard_GRS \
    --encryption-services blob \
    --https-only true \
    --min-tls-version TLS1_2 \
    --kind BlobStorage \
    --access-tier Hot

which is in fact, a name used to create storage account.

If you prefer that the variable used be _NAME, I would first update the azure plugin docs.

Once the plugin repo PR is approved and merged, we can accept this PR.