Overhaul samples

[ReubenBond]

This PR overhauls the samples in the following ways:

• All samples updated to Orleans 3.4.x
• Sample folder structure flattened - no more 1.x, 2.0, 2.1, 2.3, 3.0, 3.1, 3.3 folders
• All samples have a README.md, usually with images (screenshots, diagrams, etc)
• Top-level README.md which indexes all of the samples and describes what each one demonstrates
• Samples use .NET Generic Host with .UseOrleans instead of SiloHostBuilder
• Many samples simplified
• Added a Kubernetes sample (named Voting)

Several samples were removed:

• AdHocReactiveCaching - ideally, we could move this to a separate repository and link it from the top-level README in an Advanced Samples
• HelloWorldCpp - this C++ sample involves manually hosting CoreCLR and is too advanced for an in-repo sample. It could also be an advanced sample in an external repository

I believe we should also migrate the OneBoxDeployment sample into an external repository with a link from the top-level README. cc @veikkoeeva. I have left it where it is for now.