Adding signed byte support from cohere integration

[jonathan-buttner]

This PR is to reflect the proposed changes included in this PR: elastic/elasticsearch#104559 which adds support for the Cohere 3rd party service. By adding Cohere we also would like to support signed bytes as a response format for dense vector.

I'll leave this in draft until the elasticsearch PR is merged.

[github-actions]

Following you can find the validation results for the APIs you have changed.

API	Status	Request	Response
inference.delete_model	⚪	Missing test	Missing test
inference.get_model	🔴	1/1	0/1
inference.inference	⚪	Missing test	Missing test
inference.put_model	⚪	Missing test	Missing test

You can validate these APIs yourself by using the make validate target.

[davidkyle]

LGTM

Do you know why the validation failed for inference.get_model

[jonathan-buttner]

Do you know why the validation failed for inference.get_model

Hmm, no I'm not sure. That's weird 🤔