Add more samples, include the basic patterns

[davidmrdavid]

As in title, the current samples are too complex for a complete beginner. We should implement basic samples following the Durable patterns, or as many as we can implement with the current functionality.

[davidmrdavid]

Also add the singleton pattern from: #115

[iMicknl]

Would be good to have a sample around context.call_http(). It looks supported by the Python SDK, but can not find any samples and couldn't get it working.

https://docs.microsoft.com/en-us/azure/azure-functions/durable/durable-functions-http-features?tabs=csharp