Sample request: Nexus cancellation

[cretz]

Describe the solution you'd like

When Nexus .NET released, need sample equivalent to https://github.com/temporalio/samples-go/tree/main/nexus-cancelation and https://github.com/temporalio/samples-java/tree/main/core/src/main/java/io/temporal/samples/nexuscancellation