text: Title: [Fleet] Expose agent action service
  Body: ## Description 
  
  Currently a few plugin use action outside of Fleet (endpoint and osquery) for that they access directly the `.fleet*` indices.
  I think it will allow a better control of the data and a better maintenance if we expose an action service that allow to:
  
  - [ ] create action
  - [ ] list actions
  - [ ] list action result
  
  @pzl @patrykkopycinski  feel free to add more details on endpoint and osquery usage.
  
   