Change Nova Sonic model import and config to follow Strands docs and samples

[guiruggiero]

Amazon Bedrock AgentCore Samples Pull Request

Concise description of the PR

Changes to Nova Sonic model import and config to follow Strands [docs](https://strandsagents.com/docs/user-guide/concepts/bidirectional-streaming/models/nova_sonic/#usage) and [samples](https://github.com/strands-agents/sdk-python#bidirectional-streaming).

Checklist

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• I have reviewed the contributing guidelines
• Add your name to CONTRIBUTORS.md
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Are you uploading a dataset?
• Have you documented Introduction, Architecture Diagram, Prerequisites, Usage, Sample Prompts, and Clean Up steps in your example README?
• I agree to resolve any issues created for this example in the future.
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented

Acknowledgment

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[lanazhang]

Tested and approved.