We were previously using a mix of the "Legacy" and "YAML" steps for our Buildkite pipelines.
Now that we've moved all of the pipelines over to the "YAML" approach, we can check the files into the repo.
Once they're checked into the repo, we can "pull them" into Buildkite by replacing the contents of the pipelines in the web interface with something like:
steps: - command: buildkite-agent pipeline upload label: ":ios:"