Add ability to get deployed model for a deployment target

[aslotte]

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.