[ML] Inference API unable to retrieve inference endpoint

[jonathan-buttner]

We're seeing failures within the inference API where the internal search request is unable to retrieve the documents from the configuration and secrets indices.

Typically an error like this will be seen:

java.lang.IllegalStateException: Failed to load inference endpoint [<inference id>]. Endpoint is in an invalid state, try deleting and reinitializing the service

This could indicate that some other issue is occurring with the cluster. This is likely happening because we allow partial search results. Instead we should disable partial search results to bubble up the actual issue (whether a timeout or something else).

[elasticsearchmachine]

Pinging @elastic/ml-core (Team:ML)

[jonathan-buttner]

This might be related too: #123726