Enable SBOM generation for .NET optional workloads in Visual Studio

Visual Studio (.vsman) files need to include SBOM information as part of the VSDROP.

We likely need to look at using the updated SWIX compiler to get this support. It will likely end up in the publishing pipelines since the manifests are only generated during staging because we require all the final signed installers and VS manifests. SBOM will eventually become a required check when merging .NET insertions into VS

Alternatively we'd generate the SBOM using the .NET workload tasks, but both options need to be investigated.