Package source mapping doesn't work with Maestro added feeds

- [ ] This issue is blocking
- [x] This issue is causing unreasonable pain

Came up in https://github.com/dotnet/format/pull/1987

When using NuGet Central Package Management with more than one NuGet feed, package source mapping must be used: https://learn.microsoft.com/en-us/nuget/consume-packages/central-package-management#warning-when-using-multiple-package-sources

Unfortunately, Maestro (?) doesn't support this model as it dynamically adds feeds when producing stabilized package versions (in RTM and servicing mode). Therefore, repositories that started using CPM had to add a `NoWarn=NU1507` setting to make CPM work.

I see package source mapping as a useful feature that our infrastructure shouldn't block using. Here's some more history on this: https://github.com/dotnet/arcade/pull/9885#discussion_r915279839

cc @mmitche @ChadNedzlek