Add (or update) robots.txt and ai.txt to block AI crawlers

[sarayourfriend]

Fixes

Fixes #3900 by @zackkrida

Description

Following the advice of the blog post Zack linked (https://neil-clarke.com/block-the-bots-that-feed-ai-models-by-scraping-your-website/), I've added or updated robots.txt and added ai.txt accordingly, to block all crawlers.

As dicussed in the blog post and in #3916, this isn't a perfect solution, and there are malicious, bad-faith actors who ignore robots.txt. We'll address those using other tools at our disposal.

Docs preview pages:

• https://docs.openverse.org/_preview/4077/robots.txt
• https://docs.openverse.org/_preview/4077/ai.txt

Testing Instructions

Visit /robots.txt and /ai.txt on each of:

• the API, run just api/up. Note that robots.txt is no longer incorrectly redirected to robots.txt/ with a trailing slash. semantically the trailing slash makes no sense for a document resource, and in the worst case scenario is plausible deniability for not-entirely-bad-but-still-sketchy actors who won't follow a redirect on robots.txt.
• the documentation site, run just documentation/live and visit each
• the frontend, run just p frontend dev and check each

Checklist

• My pull request has a descriptive title (not a vague title likeUpdate index.md).
• My pull request targets the default branch of the repository (main) or a parent feature branch.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• [N/A] I added or updated tests for the changes I made (if applicable).
• [N/A] I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.
• [N/A] I ran the DAG documentation generator (if applicable).

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[github-actions]

Full-stack documentation: https://docs.openverse.org/_preview/4077

Please note that GitHub pages takes a little time to deploy newly pushed code, if the links above don't work or you see old versions, wait 5 minutes and try again.

You can check the GitHub pages deployment action list to see the current status of the deployments.

[zackkrida]

Great! I really appreciate including all of our public sites, I totally overlooked that and only considered the frontend. I'd like to try setting Crawl-delay as well but we could do that in a subsequent PR as I'm not exactly sure of an ideal seconds value yet (perhaps 30).

[krysal]

LGTM!