Leverage new project scaffolding for management-plane new service onboarding

[live1206]

For management-plane new service onboarding, we should leverage new project scaffolding instead of template. To be consistent with the behavior of DPG new service onboarding.

When this is ready, we should update https://eng.ms/docs/products/azure-developer-experience/develop/sdk-generate-mgmt-dotnet accordingly.

[welovej]

---high priority item

• [ ] xxx.Samples.csproj not generated and not included in .sln
• [ ] assets.json not generated
• [ ] <PackageId>Azure.ResourceManager.xxx</PackageId> not generated in Azure.ResourceManager.xxx.csproj
• [ ] tests/xxxManagementTestBase.cs and /tests/xxxManagementTestEnvironment.cs not generated

--low priority item

• [ ] difference: <Description> xxx.</Description> in Azure.ResourceManager.xxx.csproj
• [ ] difference: <PackageTags>xxxx</PackageTags> in Azure.ResourceManager.xxx.csproj
• [ ] difference: [assembly:Azure.Core.AzureResourceProviderNamespace("Microsoft.Template")] in Azure.ResourceManager.xxx.csproj
• [ ] difference: sdk/xxx/Azure.ResourceManager.xxx/README.md
• [ ] redundant: <TargetFrameworks>$(RequiredTargetFrameworks)</TargetFrameworks> in Azure.ResourceManager.xxx.csproj
• [ ] redundant: <IncludeOperationsSharedSource>true</IncludeOperationsSharedSource> in Azure.ResourceManager.xxx.csproj
• [ ] redundant: additionalDirectories in tsp-location.yaml
• [ ] redundant: $(RequiredTargetFrameworks) $(NoWarn);CS1591

  in Azure.ResourceManager.xxx.Tests.csproj