Add special exception for "host field is not hashable"

[NiklasBeierl]

I am adding a special exception to the es_task_handler for cases in which the "hosts" field in an elastic record is not hashable. (i.e. a dict) It seems to be a common problem, but its not really a problem with airflow itself, rather "incomaptible defaults" of airflow and filebeat. See my comment here: #15613 (comment)

I considered making _group_logs_by_host "smart" and let it handle "common" host objects. (Like the ones add_host_metadata or filebeat itself are producing)
But it struck me as risky in case someone does something else with the host field. Making an assumption like taking the host.hostname if it is available might have unintended side-effects if a worker node changes hostname / ip / Mac. Turning the entire host into a string might also cause issues if the host object happens to contain volatile values like "uptime" or "load".

closes: #15613

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[uranusjr]

Instead of linking to GitHub, we should have documentation for this.

[potiuk]

Actually better solution will be to copy the explanation to our ElasticSearch documentation (at airflow.apache.org) and link from it to there. The error message should explain the reason and link to the detailed discussion/explanation why - but linking to an issue is only fine only in a source comment, rather than in a user message. Theree we should only link to a documentation we control.

[NiklasBeierl]

Get your point, just got set up with breeze to write some proper documentation.

I have a question: airflow.providers.elasticsearch.log.es_task_handler.ElasticsearchTaskHandler has offset_field and host_field paramaters in its constructor. I have a hard time figuring out where these are being set / come from. Are they configurable?

[potiuk]

I have no idea about details of it to be hones. - I would have to - similarly to you dive deep in the code to understand it.

[potiuk]

Actually - I know that - (Re-read this) - I believe each logging handler can be configured with parameters - you can read it in "logging" configugration in our docs./

[eladkal]

@NiklasBeierl can you fix the static checks?

[github-actions]

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