[BUG] Qualification tool converts time units at task level

[cindyyuanjiang]

@amahussein found the following issue when investigating #1450:

"I found that the qualification output also has the same problem because timeUnits are converted to Milliseconds on the task level. Below is a list of some occurrences where the time units are converted on the task level (but not limited to)

• spark-rapids-tools/core/src/main/scala/org/apache/spark/sql/rapids/tool/qualification/QualificationAppInfo.scala

  Lines 170 to 174 in 993bc8f

  	private def calculateCpuTimePercent(perSqlStageSummary: Seq[SQLStageSummary]): Double = {
  	val totalCpuTime = perSqlStageSummary.map(_.execCPUTime).sum
  	val totalRunTime = perSqlStageSummary.map(_.execRunTime).sum
  	ToolUtils.calculateDurationPercent(totalCpuTime, totalRunTime)
  	}

• spark-rapids-tools/core/src/main/scala/org/apache/spark/sql/rapids/tool/qualification/QualificationEventProcessor.scala

  Lines 45 to 47 in 89fbf83

  	taskSum.executorRunTime += event.taskMetrics.executorRunTime
  	taskSum.executorCPUTime += NANOSECONDS.toMillis(event.taskMetrics.executorCpuTime)
  	taskSum.totalTaskDuration += event.taskInfo.duration

"

We should make it consistent with Profiler tool to convert from nanoseconds to milliseconds after aggregating at stage/SQL/job level.