docs: Update Bedrock documentation to show streaming example

[Amnah199]

Is your feature request related to a problem? Please describe. The BedrockGenerator now supports streaming_callback, similar to the OpenAIGenerator. After its release, it would be beneficial to include an example of 'Streaming' in the documentation to demonstrate its usage.

Describe the solution you'd like Add a separate example code for streaming, similar to the example provided for the OpenAIGenerator in the documentation: OpenAIGenerator Example.

Describe alternatives you've considered NA Additional context NA