[DOC] Update tutorials using Cohere Embedding to support v4

[tkykenmt]

What do you want to do?

• Request a change to existing documentation
• Add new documentation
• Report a technical problem with the documentation
• Other

Tell us about your request. Provide a summary of the request.
Background: Recently, Amazon Bedrock supports Cohere Embed v4, so I want to update tutorial to cover Embed v4 model. I also want to re-struct tutorials related with Amazon Bedrock. Doc hierarchy proposal as follows:

• Semantic search using Amazon Bedrock
  • Semantic search using Cohere Embed v3 on Amazon Bedrock (Existing)
  • Semantic search using Cohere Embed v4 on Amazon Bedrock (New)
  • Semantic search using Amazon Titan Text Embedding v1 on Amazon Bedrock (Existing)
  • Semantic search using Amazon Titan Text Embedding v1 on Amazon Bedrock Titan in another account (Existing)

Version: List the OpenSearch version to which this issue applies, e.g. 2.14, 2.12--2.14, or all.
2.11-

What other resources are available? Provide links to related issues, POCs, steps for testing, etc.
https://docs.opensearch.org/latest/tutorials/vector-search/semantic-search/semantic-search-bedrock-cohere/
https://docs.opensearch.org/latest/tutorials/vector-search/semantic-search/semantic-search-bedrock-titan/

Additional proposals
Titan Text Embedding v2 is already GA. I believe we can add tutorials using v2.

[tkykenmt]

I've already confirmed integration with Cohere Embed v4 and OpenSearch neural plugin works well, so I'd like to work on the issue.