Add version of SetupNugetSources that works with NugetAuthenticate

[mmitche]

• [ ] This issue is blocking
• [ ] This issue is causing unreasonable pain

In the 1ES PT migration, we need to add a version of SetupNugetSources.ps1 that works with NuGetAuthenticate. SetupNugetSources has two jobs:

• Add equivalent internal feeds and enable darc* feeds
• Add credentials for access.

Even if we switch to NuGetAuthenticate, we still need the internal and darc* feed additions. I propose adding EnableInternalNuGetSources.* which will do all the existing job of SetupNuGetSources,ps1, but without credentials. Customers would use that script instead, with NuGetAuthenticate@1 after the call.