Add manually run healthcheck DAG

[sarayourfriend]

Fixes

Fixes WordPress/openverse#1721 by @zackkrida

Description

This adds a simple DAG that takes 2 minutes to run. It is always run manually via the UI. Basically it is meant as an integration test.

I'm not sure if anything more needs to be added to this for it to be an effective test. I'll let @zackkrida and others let me know about that.

@krysal suggested that we move it into another folder, but I'm not sure where to move it. Do we need a separate folder for these type of "test/healthcheck" DAGs? If we only have one it doesn't seem worth it to me but if we're going to have more of these types of DAGs then it's probably a good idea to separate them.

Tests

Checkout this branch and run the healthcheck DAG via the UI. Be sure to to toggle the DAG to "active" state before running it (TIL!)

I didn't add unit tests for this because, well, I wasn't sure what I would test. The main function takes two minutes to run so adding a unit test for it seems like a bad idea.

Checklist

• My pull request has a descriptive title (not a vague title like Update index.md).
• My pull request targets the default branch of the repository (main or master).
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.

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[zackkrida]

Noting some things I'll want to consider when I review this:

• non provider DAGs, like the Log cleanup DAG #139 — where should we keep 'em?
• settings that seem hardcoded to assume DAGs are for image providers:
  • _DEFAULT_PROVIDER vars
  • static pull_image_data task_id in get_main_runner_operator
• integration test suite in airflow? sounds awesome to me, is it a good/bad/common/uncommon practice?

[zackkrida]

Great. My thought would be, LGTM, and then I will create a new ticket for the other considerations listed above.

[obulat]

LGTM!