Add testing for installers infra

[NikolaMilosavljevic]

Contributes to dotnet/runtime#109736

Our infra for building packages and installers for various platforms is rather complex. Making any changes in infra today, requires manual time-consuming builds of various packages in runtime and sdk, to ensure we don't introduce regressions.

The following is needed:

• Uni-tests for installers infra
• Basic testing that would exercise the main code-paths, i.e. creation of DEB/RPM packages and static analysis of package contents and metadata