bug: remove duplication in mlflow-using stacks

[lukemarsden]

We have a few stacks that are using mlflow, but they're currently just using copies of the helm chart.

Move mlflow into its own top level component (exists but empty https://github.com/combinator-ml/terraform-k8s-mlflow)

Publish it to terraform registry. (@philwinder do you have a guide on how to do this?)

Replace the usage in:

• https://github.com/combinator-ml/terraform-k8s-stack-kubeflow-mlflow and
• https://github.com/combinator-ml/terraform-k8s-stack-bodywork-mlflow

With reference to the module like this:

• https://github.com/combinator-ml/terraform-k8s-stack-pachyderm-minio/blob/main/stack.tf#L14-L18

[philwinder]

In progress.