[DOC] Add support for Bedrock Converse API

[austintlee]

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Tell us about your request. Provide a summary of the request.
ml-commons is adding support for Bedrock Converse API that allows RAG users to gain access to the latest LLMs from Anthropic, i.e. Claude 3.5 sonnet. In addition, this will also work with OpenAI GPT 4o for including images in chats.

*Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.

[austintlee]

We are introducing a new RAG search processor parameter called "llm_messages". This is intended to match one-to-one the "messages" parameter of the Bedrock Converse API (https://docs.aws.amazon.com/bedrock/latest/APIReference/API_runtime_Converse.html) and therefore, an array of messages (llm_messages) passed to the RAG search processor will be converted to an array of Message objects and passed to Bedrock.

llm_messages = [ MessageBlock ] ([] representing the array notation)
MessageBlock = { "role": , "content": [ ContentBlock ] }, role = "user" | "assistant" (this is typically "user", but you can interweave "user" and "assistant" for few-shot prompting)
ContentBlock = {"type": <content_type>, <content_type>: <content_detail>}

content_type = "text" | "image" | "document"
For "text":
content_detail = "string"
For "image":
content_detail = {"format": ..., "type": ..., "data": ... }
For "document":
content_detail = {"format":..., "name": ..., "data": ...}

Example 1: text
llm_messages: [{"role": "user", "content": [{"type": "text", "text": "what is the tallest building in the world?"}]}]

Example 2: image
llm_messages: [{"role": "user", "content": [{"type": "text", "text": "use the image to answer the following question: how many apples are in the tree?"}, {"type": "image", "image": {"format": "jpeg", "type": "data", "data": ....}}]}]

Example 3: document
llm_messages: [{"role": "user", "content": [{"type": "text", "text": "what is the average of the third column in the table on page 1 of the attached document?"}, {"type": "document", "document": {"format": "pdf", "name": "many_tables", "data": ....}}]}]

[austintlee]

llm_model prefix must be "bedrock-converse/", e.g. llm_model: bedrock-converse/anthropic.claude-3-sonnet-20240229-v1:0

[austintlee]

Example 4: text + image + document

[Naarcha-AWS]

@austintlee: Can you submit a PR with these updates?

[austintlee]

I'll do that today.

We already have a page that explains all the parameters, but I don't know if this needs a dedicated/separate page.

[Zhangxunmt]

@Naarcha-AWS, please remove the 2.17 tag since this feature is not included in 2.17 anymore.