Show running task logs in the UI with Elasticsearch remote logging

[aeroyorch]

Running task logs were not shown in the airflow UI when using elasticsearch remote
logging, and only appeared once the task had finished. In Airflow 3 the supervisor
uploads logs to elasticsearch only after the task finishes, and the elasticsearch
handler reads only from elasticsearch, so a running task had nothing to display.

Fix:

For airflow 3, running and deferred tasks (current attempt) now delegate to the base
FileTaskHandler._read, which serves the live worker and executor logs and drives
end_of_log from the task state, similar to what is done by the S3/GCS backends.

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Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Claude Opus 4.8 for inspecting other providers' code (GCS/S3).

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[aeroyorch]

cc @eladkal @Owen-CH-Leung