Defines new inference_user and inference_admin roles with the
related cluster privileges manage_inference and monitor_inference.
inference_user can list the models and preform inference,
inference_admin can do the same plus create and delete models
Makes the task_type element of the _inference API optional so that
it is possible to GET, DELETE or POST to an inference entity without
providing the task type
* [DOCS] Creates documentation structure.
* [DOCS] Adds PUT inference API docs and part of GET inference API docs.
* [DOCS] Fixes complaining CI.
* [DOCS] Adds GET and DELETE API docs for inference API.
* [DOCS] Adds POST inference API docs.
* Apply suggestions from code review
