Docker Swarm Mode has been in severely declining usage and maintenance for years now. Meanwhile, Docker Compose has had quite a lot of changes (notably deprecating the `version:` field required by Swarm / forward compatibility). As a result, it no longer makes a ton of sense for us to prefer/suggest Swarm usages.
This changes all references to be `compose.yaml` (the upstream-preferred canonical filename: 9a9cc5d9c3/cli/options.go (L384-L385)) directly, leaving "swarm compatibility" as an exercise for the minority of readers who might still need/want it.
Unfortunately, this also means we need to remove all the play-with-docker links (since it only supports stack deploy via URL arguments, not compose), but my experience with that service is that it hasn't been terribly performant for a while, so I don't think this is a huge loss.
(There were also a few trailing references to the long-since-defunct Docker Machine project which have also been cleaned up.)
This should make it much faster to find the right place to file issues, get help, find out whether upstream maintains an image, etc.
I've done my best to represent each `REPO/maintainer.md` file appropriately, but I might have missed some (or there might be something else a maintainer prefers be listed there, either more or less descriptive, for example), which would be welcome contributions following this change.
We either need to explain that this is maintained by the Docker community or pull the image from docker. We are getting push back on our side about this.
I tested this by using `docker-compose up -d`, going through Drupal's web-based setup process to get Drupal fully configured and operational, then used `docker-compose up -d --force-recreate` to force both containers to be re-created (which works very hard to keep the volumes), and verified that my site was still configured and working properly.