Improve the `task_settings` parameter's description

[kosabogi]

Affected pages:
https://www.elastic.co/docs/api/doc/elasticsearch/v9/operation/operation-inference-sparse-embedding
https://www.elastic.co/docs/api/doc/elasticsearch/v9/operation/operation-inference-completion
https://www.elastic.co/docs/api/doc/elasticsearch/v9/operation/operation-inference-stream-completion
https://www.elastic.co/docs/api/doc/elasticsearch/v9/operation/operation-inference-text-embedding

Body parameter - task_settings: The new description is only “Optional task settings”, the old one was more descriptive: “Task settings for the individual inference request. These settings are specific to the <task_type> you specified and override the task settings specified when initializing the service.”