Check if resource exists

**feature request**
currently creating AKS cluster using `Microsoft.MachineLearningServices/workspaces/computes` is not idempotent and will error if the link already exists. Currently there is no convenient way to check if the resource already exists and would like to understand the best way to handle this scenario in Bicep

Docs Link: https://docs.microsoft.com/en-us/azure/machine-learning/how-to-create-attach-kubernetes?tabs=python#limitations

**Describe the solution you'd like**
Convenient way to check if the resource exists and skip certain action ( in this case dont try to establish link) . This could be achieved using a deployment script az cli to see if the resource exists, but looks heavy for a simple check