Add RetryPolicy to ActivityHeartbeatingCancellation sample

[aneetakolhe]

What was changed

This PR enhances the existing ActivityHeartbeatingCancellation sample by
demonstrating how Activity heartbeats can be combined with RetryPolicy
configured at the workflow level.

Why?

This helps .NET developers understand best practices for long-running,
resumable activities.

Checklist

• Add RetryPolicy to the activity execution in MyWorkflow
• Ensure heartbeat progress is sent from the activity
• Update README to explain how retry and heartbeats work together

1. Closes

2. How was this tested:
   Documentation change

3. Any docs updates needed?

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[cretz]

This seems to be incomplete and we don't use "temporalite" (other samples say to look at primary README for prerequisites to setup server)

[aneetakolhe]

Thanks, agreed. I’ll align this README with other samples by removing the temporalite mention and pointing to the primary README prerequisites for running a Temporal server.

[cretz]

I wonder if this really deserves to be a sample though. It's simply showing how to change two defaults for a RetryPolicy property, correct? Not sure it relates to heartbeat/cancellation or that it deserves a sample to show how to set retry policy settings.

[aneetakolhe]

Thanks for the feedback to all comments. Makes sense. I understand the desire to keep the sample narrowly focused.
I’ll close this PR. Appreciate the review and discussion.

[cretz]

Heartbeating sample seems unrelated to retry settings that you may want to set whether or not you heartbeat. Is this addition to the sample only for showing that you can set the RetryOptions property? This can be set regardless. I am not sure it makes sense in a heartbeating/cancellation sample to demonstrate that this setting can be set (any more than any other activity option setting).

[cretz]

Two of these are the defaults already, and the other two are just choices a user may make regardless of heartbeating/cancellation.