Adding MLFlow API for creating model versions

What does this MR do and why?

Continuing on the work to build the MLFlow Model Versions API, this MR adds an endpoint to create a model version for a given model name.

The Create ModelVersion API accepts a name and description, and it returns a ModelVersion object, or an error message if the validation fails.

Note: this MR is a partial implementation of the MLflow spec. Additional input parameters will be supported in follow up MRs.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.