Samples for creating privateendpoints

Currently, no samples available for creating a private endpoint for already existing services. It would be great if you can create one.

1. https://github.com/Azure/azure-sdk-for-go/blob/master/services/network/mgmt/2020-06-01/network/privateendpoints.go
2. https://github.com/Azure/azure-sdk-for-go/tree/master/services/network/mgmt/2020-06-01/network
3. https://github.com/Azure/azure-rest-api-specs/blob/master/specification/network/resource-manager/readme.go.md
4. https://github.com/Azure/azure-rest-api-specs/tree/master/specification/network/resource-manager/Microsoft.Network/stable/2020-07-01

Start by reading services/network/mgmt/2020-06-01/network/privateendpoints.go and the surrounding network package, then compare the Azure REST API specification links provided. Add a Go sample showing creation of a private endpoint for an already existing service, with the sample's successful execution as the completion check.

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