Amazon Bedrock AgentCore Samples - Update short term memory examples to use Memory MAnager

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

```
Update short term memory examples to use MemoryManager
```

**Is this feature already supported by the AgentCore service?**
- [x] Yes
- [ ] No

If `yes`, please provide any appropriate documentation link.
https://docs.aws.amazon.com/bedrock-agentcore/latest/devguide/using-memory-short-term.html