insights: FE address unhandled insight types

Created by: unclejustin

For context: https://github.com/sourcegraph/sourcegraph/pull/27431#issuecomment-966504705

In the getInsightView mapping function we parse out and map an object based on insight.presentation.__typename. We need to handle an "unsupported" type. Probably by throwing an error in the default case of the switch.