[azure arm] Be able to change storage type before managed image is created

_This issue was originally opened by @frankzo as hashicorp/packer#9535. It was migrated here as a result of the [Packer plugin split](https://github.com/hashicorp/packer/issues/8610#issuecomment-770034737). The original body of the issue is below._

### Feature Description

We would like to be able to build using a Azure Premium_LRS disk but after the build is ready we would like to store it as Standard_LRS obviously to save costs while maintain multiple versions.

#### Use Case(s)

We build images that benefit greatly from Premium_LRS since build-time is cut in half for some images. Premium_LRS comes with a higher price than Standard_LRS; it makes sense to store the images files as "Standard_LRS" since we are pushing to the Image Gallery too and we only maintain a few versions of the Image resource.