Add ability to get deployed model for a deployment target

**Is your feature request related to a problem? Please describe.**
We need the ability to get the run, registered model and metrics for a model currently deployed to production.

**Describe the solution you'd like**
We should add two methods

- `GetDeployedModel(string experimentId, DeploymentTarget deploymentTarget)`
- `GetRunOfDeployedModel(string experimentId, DeploymentTarget deploymentTarget)`
- `GetDeployedModel(string experimentId)` <- this should fetch the model deployed to production if any
- `GetRunOfDeployedModel(string experimentId)` <- this should fetch the Run of a model currently deployed to production

The last method should return a `RegisteredModel` for the deployment target populated with the `Run` and all `Metrics` etc.