Support Package Source Mapping when managing feeds through darc/Maestro

[premun]

Context

We should support PSM when modifying repos using CPM as described in #3002. Without this feature, repos cannot specify where packages should come from. This is a security feature. Without this feature, the repos need to bypass a build warning NU1507.

Goal

When modifying nuget feeds (e.g. stable feeds being added during dependency updates), we need to also modify the accompanying PSM section in NuGet.config.