[Samples] Samples repository maintenance

[vlada-shubina]

There is a samples repository: https://github.com/dotnet/dotnet-template-samples

Decide:

• if we are going to maintain it? Now it is archived.
• should we bring it to main repository?
• should we accept requests for new examples there

Originally posted by @bozturkMSFT in #2518 (comment)

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We agreed to move examples to dotnet/templating repo instead.
The examples should be part of separate project containing all the templates.
The tests (using test framework) should be added to verify the examples can be run and produce correct output - as a separate test project.
After it is done, we should update links in the documentation to a new location in templating repo.

[vlada-shubina]

@mmitche
we are considering bringing https://github.com/dotnet/dotnet-template-samples back to life as it is proved to be very useful resource for community.

1. Is "unarchiving" it an option to consider? we can own that repo and update the samples there and possibly add them to our CI.
2. If answer to 1. is no, is it possible to unarchive it for a while so we can reference sample in their new location in dotnet/templating repo readme.md over there.

Thanks.

cc @KathleenDollard @DavidKarlas