[REQUEST]: Inference API removing references to the _unified URL suffix

[jonathan-buttner]

Description

What: Currently in the docs we have an inference API route called the chat completion route. The URL for this route requires the suffix to be _unified (_inference/chat_completion/<id>/_unified).

We'd like to rename this suffix to _stream.

When: We'd like this to be in the docs for the 8.18 and 9.0 releases.

Why: The _unified suffix is confusing to uses as it doesn't really explain why it is unified. We'd like to keep with the streaming route we already have.

Resources

This feature was initial created in this PR: elastic/elasticsearch#118696 (docs)
Feature PR: elastic/elasticsearch#117589

I have a PR to incorporate the changes from _unified to _stream here: elastic/elasticsearch#121078

I need that PR merged before I can merge a client spec PR here: elastic/elasticsearch-specification#3545

See this comment: elastic/elasticsearch-specification#3545 (comment)

Which documentation set does this change impact?

Elastic On-Prem and Cloud (all)

Feature differences

There are no differences

What release is this request related to?

8.18

Collaboration model

The engineering team

Point of contact.

Main contact: @jonathan-buttner

Stakeholders:

Notes

I'm not sure what needs to happen to ensure that the changes in the ES PR get propagated through to the new docs system. I'm happy to make changes to my ES PR to assist with that though.