[Logs UI] Support partitioned jobs in the log entry rate results API

[weltenwort]

Summary

The log rate analysis results API implemented in #42057 should be adapted to support returning the results of partitioned jobs.

Acceptance criteria

• The below response has been validated to be compatible with the requirements of the UI and the result data provided by the ML jobs.
• The response of the /api/infra/log_analysis/results/log_entry_rate route implements the following interface:

interface GetLogEntryRateSuccessResponse {
  data: {
    // length of a bucket in milliseconds
    bucketDuration: number;
    // a sequence of non-overlapping time buckets in ascending order
    histogramBuckets: Array<{
      // a set of data sets that analysis has been partitioned into
      dataSets: Array<{
        // the number of underlying buckets used in the analysis
        analysisBucketCount: number;
        // a set of anomalies found within this bucket and data set
        anomalies: Array<{
          // the number of log entries actually found
          actualLogEntryRate: number;
          // a relative measure of the anomalousness
          anomalyScore: number;
          // duration of the anomaly in milliseconds
          duration: number;
          // start of the anomaly as an epoch timestamp in milliseconds
          startTime: number;
          // the number of log entries typically found according to the model
          typicalLogEntryRate: number;
        }>
        // the average actual log entry rate
        averageActualLogEntryRate: number;
        // the data set id
        dataSetId: string;
      }>;
      // start of the bucket as an epoch timestamp in milliseconds
      startTime: number;
    }>;
  };
}

[elasticmachine]

Pinging @elastic/infra-logs-ui