Onboard maintenance-packages to source-build

[ericstj]

Describe the Problem

The https://github.com/dotnet/maintenance-packages repository is being created as a place for packages that are still in support but no longer built elsewhere to continue to build.

The packages produced here will be referenced by packages that are part of the product on down-level platforms (eg: .NETFramework, .NETStandard).

Rather than copy the packages from here to SBRP, we should consider bringing maintenance-packages into source-build.

Describe the Solution

Onboard maintenance-packages into source-build and allow it's packages to flow into runtime and other repos. Note that maintenance-packages isn't expected to branch with the product, but instead be in perpetual LTS. As such its expected that tip will always be correct for all versions of .NET that are still in support.

Additional Context

dotnet/runtime#108806

cc @ViktorHofer @carlossanlop

[dotnet-issue-labeler]

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[dotnet-issue-labeler]

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[ViktorHofer]

I think that would mean that the maintenance-packages repo would need to be added to the VMR.

[MichaelSimons]

Adding new repos to source-build is a repo owner responsibility - it is intended to be a self-servicing task. @dotnet/source-build will certainly provide guidance when needed.

[ericstj]

I think that would mean that the maintenance-packages repo would need to be added to the VMR.

Not necessarily. There are other repos t hat are part of source build but not vmr.

[MichaelSimons]

Not necessarily. There are other repos t hat are part of source build but not vmr.

I'm not following. Source build works on the VMR so by definition, everything that is source-built must be part of the VMR.

[MichaelSimons]

Closing per the discussion in dotnet/maintenance-packages#140. Summary: maintenance-packages is not required in SB. SBRP satisfies the requirements.