[Azure Mgmt Generator] The `Create` operation for a resource should always have the `CreateOrUpdate` name

[ArcturusZhang]

In the azure mgmt generator, the name for create operation is taking its name in the spec, which is inconsistent with our old generator which is hard-coded to always be CreateOrUpdate.

This work should be done inside the eng/packages/http-client-csharp-mgmt project.