Support server-side generation of services with models, service traits

To help Azure service teams generate Rust-based services from TypeSpec - to help ensure the TypeSpec is correct by starting with spec-driven development and using our [Azure.Core](https://azure.github.io/typespec-azure/docs/libraries/azure-core/reference/) and [Azure.ResourceManager](https://azure.github.io/typespec-azure/docs/libraries/azure-resource-manager/reference/) modules - create an MVP that generates models for both serialization and deserialize (full) as well as traits with required functions that services must implement.

This initial version isn't concerned with service implementation. Services teams are experimenting with different backends, and keeping written code working is critical. But by implementing a trait, they can at least help get the service model right. The hope is that this incentivizes teams to start with TypeSpec and we won't have to have long (or any?) REST API reviews and approved suppressions because it's too late to reasonably change prior to release.