Is your feature request related to a problem? Please describe.
A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
Model Registry has it's own REST API, but a domain model very similar to MLflow. Model Registry is also going to add support for Experiment Tracking in another enhancement request #1224 .
MLflow SDK supports loading plugins for integrating with other tracking and registry stores.

Model Registry MUST implement an MLflow plugin to allow millions of existing MLflow users to seamlessly use Model Registry for experiment tracking to begin with. Support for Registry API/store can be added in the future.

Describe the solution you'd like
A clear and concise description of what you want to happen.
Implement an MLFlow tracking store for tracking experiments and runs.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.
Implementing a gRPC server in the Model Registry service compatible with MLflow gRPC API was also considered. But, it complicates the existing Model Registry service implementation. It's easier to use MLFlow plugin architecture and directly make calls to existing Model Registry REST API.

Additional context
Add any other context or screenshots about the feature request here.