A warning should be provided if there are unexpected properties defined in yaml

We recently have added some new features to the yaml schema (e.g. `beforeJob`, `sources`) which will change the way that the crank controller loads and reads the crank yaml file. It would be good if the controller is able to check if the yaml contains any properties which it does not know about to tell the user that they may need to update their crank controller so that it can handle these properties correctly.

This change can be done by updating the [benchmarks.schema.json](https://github.com/dotnet/crank/blob/main/src/Microsoft.Crank.Controller/benchmarks.schema.json) to the latest version of the schema and ensuring that we always keep it up to date going forwards whenever we update the yaml. We would then need to change the validation code that uses this schema to display a warning if it sees any unexpected properties.

As a further extension point, we could also make the crank controller make a query to nuget to see if a new version of crank exists to tell people if a new one exists and how to upgrade to it.