Make Elasticsearch/OpensearchTaskHandler to render log well

[Owen-CH-Leung]

closes: #53526

As described in the issue, the existing ElasticSearchTaskHandler / OpensearchTaskHandler does not render log well. As compared to local task log rendering, we can see that local task log is able to render logs such that it's filterable by log level.

The root cause is that the handler is grouping all log lines into a single StructuredLogMessage. Instead of grouping, each log line should form its own StructuredLogMessage.

airflow/providers/elasticsearch/src/airflow/providers/elasticsearch/log/es_task_handler.py

Lines 385 to 387 in 12b4843

	message = header + [
	StructuredLogMessage(event=concat_logs(hits)) for hits in logs_by_host.values()
	]