Removes version from docker-compose.yaml (#479)

# Description

This choice is related to the [deep history of docker
compose](https://docs.docker.com/compose/intro/history/). Previously we
had a `version` specification in the `docker-compose.yaml`. While I did
this initially to ensure support for extensions, I think it could
confuse users about which version of docker compose is supported. I
believe we should only support the most modern version of docker compose
(this is what we direct people to install), which is the plugin version
of docker compose (invoked in the cli as `docker compose` rather than
`docker-compose`) and the [Compose
Specification](https://github.com/compose-spec/compose-spec) which is
backwards compatible with much of versions 2+3, but which is its own
format.

This hasn't yet caused a problem per-se, but could mislead people about
which Docker setup we support.

## Type of change

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applicable. -->

- Bug fix (non-breaking change which fixes an issue)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./orbit.sh --format`
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have run all the tests with `./orbit.sh --test` and they pass
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

<!--
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putting an x character in it

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- [x] I have done this task
- [ ] I have not done this task
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docker/docker-compose.yaml

-version: "3.4"
 # Here we set the parts that would
 # be re-used between services to an
 # extension field