Amazon Bedrock AgentCore Samples - [Example Request]

**Describe the tutorial request**
A clear and concise description of what is being requested.

```
Changes to add async WAT refresh sample under 03-AgentCore-identity, because long-running threaded agents lose the WAT after JWT expiration, causing orphaned workload identities. This sample demonstrates a companion library that propagates WAT to threads and coordinates refresh with the client.

```

**Is this feature already supported by the AgentCore service?**
- No

If `yes`, please provide any appropriate documentation link.