add delete anomaly results API

[ylwu-amzn]

Description

With historical analysis, user can generate much more anomaly result in a short time, especially for HC detector. AD plugin will roll over anomaly result index if its doc count reaches some limit, and will delete roll-over index after some period (30 days by default). So if user run historical analysis, it may generate too many AD results and speed up the rollover and AD result index cleanup.

This PR adds delete anomaly result API. User can use this API to delete anomaly results with specific query like delete all anomaly results of one detector/task.

Sample request

DELETE _plugins/_anomaly_detection/detectors/results
{
  "query": {
    "bool": {
      "filter": [
        {
          "term": {
            "detector_id": {
              "value": "6tZminoBaXxjTubPk0k6"
            }
          }
        }
      ]
    }
  }
}

Issues Resolved

[List any issues this PR will resolve]

Check List

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[zhanghg08]

A high level comment, do we need to consider FGAC with delete api?

[ylwu-amzn]

A high level comment, do we need to consider FGAC with delete api?

Yes, check DeleteAnomalyResultsTransportAction.java line 79

addUserBackendRolesFilter(user, request.getSearchRequest().source());

This method adds user backend role filter, so users can only delete anomaly results which they have permission.

[zhanghg08]

LGTM!

[spbjss]

client.execute() will be called anyway?

[ylwu-amzn]

Yes, split the code branch clearly to make it more readable.

[spbjss]

looks good to me.