add standard Skus_List API support

### Clear and concise description of the problem

It is documented internally at [ARM SKU API Contract with Customer.](https://armwiki.azurewebsites.net/api_contracts/SKUContract.html#arm-sku-api-contract-with-customer). The Azure VMware Solution already supports the API, but I'm having a bit of trouble putting together the TypeSpec for it in https://github.com/Azure/azure-rest-api-specs-pr/pull/20131 . Like the Operations API, I would prefer not to use a common definition.

### Checklist

- [x] Follow our [Code of Conduct](https://github.com/azure/typespec-azure/blob/main/CODE_OF_CONDUCT.md)
- [x] Check that this issue is about the Azure libraries for typespec. For feature request in the typespec language or core libraries file it in the [TypeSpec repo](https://github.com/Microsoft/TypeSpec/issues/new/choose)
- [x] Read the [docs](https://azure.github.io/typespec-azure/).
- [x] Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

Start by reviewing the linked ARM SKU API Contract and the TypeSpec work in azure-rest-api-specs-pr#20131, then compare it with the existing Operations API support. Done means standard Skus_List API support is represented in TypeSpec without using a common definition.

Written by the indexing model from the issue text.