Enable arcade -sign functionality in runtime

[mmitche]

Right now runtime uses a bit of custom infra to sign (a separate job that gathers intermediate artifacts and signs them). For the VMR, it also needs to support the ability to do the traditional arcade-based signing. When -sign is passed, Sign.proj is invoked, items to sign is populated, etc. etc.

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[ViktorHofer]

@jkoritzinsky please see my PR #100004 which does a lot of what we want here. We don't need the PostBuildSign & SignAndPublishAsJoinPoint stuff in it anymore now, but everything else uses the Arcade integration.