read timestamp from Cloudwatch events

[pavelhlushchanka]

Related: #15144. That's my first pr. Here is the main idea of the feature. The handler reads the timestamp of Cloudwatch events. So timestamp can be seen on the Log page of the task. Also I wanted to add a support of DEFAULT_UI_TIMEZONE here. Basically to format UTC timestamp with respect to specified UI timezone. However i found only the code that resolves DEFAULT_TIMEZONE. So i used it for now. Also i'm making event_dt as naive right before formatting in order to remove timezone information in logs.

So my main question is is it fine to use DEFAULT_TIMEZONE for formatting of the timestamps? Or there should be similar resolver for DEFAULT_UI_TIMEZONE and timestamps are formatted with respect to specified ui timezone?

[boring-cyborg]

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[pavelhlushchanka]

I've checked the default formatting of the timestamp in logs. Basically timestamp is formatted based on UTC regardless what timezones are specified in the config. So I decided to have a consistent behaviour here. Also I applied the same default formatting template.

[feluelle]

LGTM 👍

You could also explicitly add UTC to the string or use well-known ISO-8601 format.

[github-actions]

The PR is likely OK to be merged with just subset of tests for default Python and Database versions without running the full matrix of tests, because it does not modify the core of Airflow. If the committers decide that the full tests matrix is needed, they will add the label 'full tests needed'. Then you should rebase to the latest master or amend the last commit of the PR, and push it with --force-with-lease.

[pavelhlushchanka]

@feluelle thanks for the review. I decided to not include timezone for the sake of being consistent with the default timestamp format

[boring-cyborg]

Awesome work, congrats on your first merged pull request!