[ES|QL] Support CCS for inference commands

[afoucret]

Closes #136860

This PR add CCS support for ES\QL query that are using an inference command (RERANK and COMPLETION) or an inference function (TEXT_EMBEDDING).

The inference is always executed on the coordinator cluster, meaning that the endpoint need to exists on the coordinator clusters.

[elasticsearchmachine]

Pinging @elastic/es-search-relevance (Team:Search Relevance)

[elasticsearchmachine]

Hi @afoucret, I've created a changelog YAML for you.

[github-actions]

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[ioanatia]

code changes look alright, but IMO it would be easier if we get the usage limits changes first.
this way we know there's always a LIMIT before the inference plans.

[ioanatia]

no need to add a new dataset, just use the existing dense_vector one.

[ioanatia]

Have we checked that there's no way to get to a place where we have an unexecutable plan?
IMO we should verify that there is a pipeline breaker before any of the inference plans.

[github-actions]

🔍 Preview links for changed docs

• docs/internal/DistributedArchitectureGuide.md
• docs/reference/elasticsearch/rest-apis/retrievers/diversify-retriever.md
• docs/reference/query-languages/esql/kibana/docs/functions/chunk.md

[afoucret]

Replaced by #139244