[Transform] Expose authorization failure as transform health issue

[przemekwitek]

This PR enhances the _stats API with the information about the latest authorization failure, i.e. whether the authorization was successful or not, and if not, what was the error.
This information is presented as a TransformHealthIssue under health object.
With this PR, the response of the _stats call will contain:

{
  ...
  "health": {
    "status": "green"
  },
  ...
}

if the last authorization was successful.

or

{
  ...
  "health": {
    "status": "red",
    "issues": [
      {
        "type": "privileges_check_failed",
        "issue": "Privileges check failed",
        "details": "Cannot create transform [my-transform] because user bob lacks the required permissions [my-source-index:[read, view_index_metadata], my-dest-index:[index, read]]"
      }
    ]
  },
  ...
}

if the last authorization was unsuccessful.

Relates #93259

[przemekwitek]

run elasticsearch-ci/docs

[przemekwitek]

run elasticsearch-ci/packaging-tests-windows-sample

[elasticsearchmachine]

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

[elasticsearchmachine]

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

[droberts195]

LGTM