Adding support for multiple hostnames in Task Instances

[pavel-lexyr]

This PR aims to fix a long-standing logging bug present in Airflow. In particular, any clusters of more than one worker do not handle their logs appropriately - always fetching files from the host used in the last run.

This change replaces the hostname field of the TaskInstance object with a list hostnames, storing a separate hostname for each run of the job.

This iteration is not final. If you have any comments, do not hesitate to post them.

In particular, the areas I am looking for feedback on are:

• Is the AIP process necessary for this kind of change? If so, how would one ensure it goes smoothly?
• What kinds of tests should be added?
• A database migration is needed for this change. What is the appropriate way to implement one?

closes: #16472

^ Add meaningful description above

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[boring-cyborg]

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[uranusjr]

Instead of trying to implicitly looking up the correct hostname based on try_number, it may be better to introduce a new table altogether to keep the (dag_id, task_id, run_id, try_number) -> hostname lookup. Or a dict (via JSON column).

[pavel-lexyr]

That's a reasonable idea. I'll close and restart it as a different PR.