Add envfile rotation DAG

[sarayourfriend]

Fixes

Fixes https://github.com/WordPress/openverse-infrastructure/issues/968 by @sarayourfriend

Description

Adds a DAG to rotate the envfiles in the environment files buckets. The DAG finds the 3 most recent envfiles for each service, and then deletes everything else in the buckets.

Drafted because I'm still trying to understand how best to test this. @stacimc @AetherUnbound if either of y'all have any input/ideas about how to test this, please let me know. I've tried changing the AWS connection locally to test the listing logic, but Airflow expects to be able to write logs to S3 using those same connection credentials, so the tasks fail immediately when they can't write to the logs bucket. Should I give up trying to test against the real buckets and just mock responses out in unit tests? That's about as good as just trying to run it in production and seeing what happens, as it'll depend entirely on whether I get the mocks right... and there's no sure-fire way to test that with our current tools, as far as I know. I've seen this moto library mentioned around before as a good way to mock AWS resources but we don't use it at all, and it's missing implementation for describe_launch_template_versions anyway... it might still be useful for other parts.

Let me know what y'all think. I'll leave this drafted until then/until I come up with something on my own. Thanks in advance.

Testing Instructions

TBD.

Checklist

• [x] My pull request has a descriptive title (not a vague title likeUpdate index.md).
• [x] My pull request targets the default branch of the repository (main) or a parent feature branch.
• [x] My commit messages follow best practices.
• [x] My code follows the established code style of the repository.
• [ ] I added or updated tests for the changes I made (if applicable).
• [x] I added or updated documentation (if applicable).
• [x] I tried running the project locally and verified that there are no visible errors.
• [ ] I ran the DAG documentation generator (ov just catalog/generate-docs for catalog PRs) or the media properties generator (ov just catalog/generate-docs media-props for the catalog or ov just api/generate-docs for the API) where applicable.

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