Allow MD_JSON for bedrock client

[RohanJnr]

Bedrock models such as Kimi K2 Thinking usually return ... tags which precedes the actual JSON data. Currently instructor retries and eventually the model returns the JSON only.

It would be great if we could use MD_JSON or custom processors to handle removing such tags.

Additional context
Using version = "1.14.5"

I did notice in the documentation that BEDROCK_JSON is legacy and replaced by MD_JSON but I still don't find doc to replace it in code or find a solution to the problem I have described

[jxnl]

Related: #2084 covers adding native Bedrock structured outputs support more broadly, which would also address the MD_JSON use case for models like Kimi K2 Thinking that return content in tags before JSON.

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