BedrockAgentRuntimeAsyncClient InvokeAgent Attributions ALWAYS Empty

### Describe the bug

I have an agent linked to a knowledge base that uses the Claude 3.5 Haiku model to orchestrate response.

I can't get the attribution information containing retrieved references to pass all the way through.
Whenever I'm looking at the attribution property on my PayloadPart object in the visitChunk method it's always null.

What's interesting is, if I query the Knowledge Base directly using the same model in the AWS console, I get the attribution's references in-line exactly how I want. When I go up to the agent level, those attributions are dropped in the response even though they're still clearly available in the trace.

### Regression Issue

- [ ] Select this option if this issue appears to be a regression.

### Expected Behavior

I'd expect the attribution information to pass all the way through to the request's response.

### Current Behavior

I get a good response from the agent but there is no attribution info. The attribution property is null.

### Reproduction Steps

Send any InvokeAgent request to an agent using a knowledge base and Claude 3.5 Haiku. Investigate the attribution property on the PayloadPart when visitChunk is called on the response.

### Possible Solution

_No response_

### Additional Information/Context

This same issue appears to be occurring in boto3 as well:

https://github.com/boto/boto3/issues/4197

### AWS Java SDK version used

2.30.3

### JDK version used

openjdk version "21.0.5" 2024-10-15 LTS OpenJDK Runtime Environment Temurin-21.0.5+11 (build 21.0.5+11-LTS) OpenJDK 64-Bit Server VM Temurin-21.0.5+11 (build 21.0.5+11-LTS, mixed mode, sharing)

### Operating System and version

Ubuntu 22.04.5 LTS