[DOC] Update Cohere Connector documentation (v3 and PQ guidance)

[dylan-tong-aws]

What do you want to do?

• [ x] 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 and all versions that are affected.

Update the Cohere connector documentation: https://opensearch.org/docs/latest/ml-commons-plugin/remote-models/connectors/#cohere-connector

1. Update the blueprint to use the latest version for cohere embed v3. Please work with @ylwu-amzn to obtain the latest blueprint. I can't find it in Github, and there are no examples in the documentation.

2. Add a section for PQ support guidance:

Cohere embed v3 has been tuned for IVF PQ index support (https://opensearch.org/docs/latest/search-plugins/knn/knn-index/#supported-faiss-encoders). The following default parameters should work well:

code_size=8 Cohere recommend m=256 (for a 16x compression) or m=128 (for a 32x compression).

As similarity_metric, cohere has tested and tuned the model inner product

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

[ylwu-amzn]

Cohere embed blueprint (v2 and v3): https://github.com/opensearch-project/ml-commons/blob/2.x/docs/remote_inference_blueprints/cohere_connector_embedding_blueprint.md

[hdhalter]

Thanks, @dylan-tong-aws and @ylwu-amzn ! Is this connected to a release?

[ylwu-amzn]

Cohere Connector documentation

This part is not for 2.13 release. It's just a doc for released feature.

[hdhalter]

This PR addresses the first item above: https://github.com/opensearch-project/documentation-website/pull/6671

[hdhalter]

The first item is merged. I'm working with jmazane on the second item.

[hdhalter]

@jmazanec15 - Did we address #2 above?