New rule: api-version parameter should define an enum with the possible api-versions

Based on feedback in PR https://github.com/Azure/azure-rest-api-specs-pr/pull/309/files#r156773386 it'd be good to have a linter rule that recommends (at least warning) to have an enum defined for the api-version parameter, which would be a constant (in generated code) if there's only one value, or include all the possible api versions. We should also check that x-ms-enum extension exists with modelAsString=true as it's a value that will grow.
It may also be good to have a default value defined for this enum.