Testing of packages and installers and related infra

[NikolaMilosavljevic]

This covers packages and installers for all .NET repos (i.e. SDK) and not just runtime.

Our infra for building packages and installers for various platforms is rather complex. There is some basic automated testing in SDK repo that is currently included in regular build. This will be removed as part of updating SDK's build to use new Deb and Rpm infra, i.e. dotnet/sdk#43688

Testing should cover the following:

• Installation of packages and installers
• Execution of scenario tests
• Unit-tests for installers infra
• Static tests for package contents, i.e. metadata

Each of these should have its own tracking issue.

Tracking issues:

• Add testing for installers infra arcade#15251
• Add tests for installers and packages runtime#109848

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

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