Add option to skip external lookup where local user does exists

[hikalkan]

Add a property named SkipExternalLookupIfLocalUserExists, true by default. If this is true, we should call external service only if requested user is not present in the local repository (db). This will reduce service-to-service calls. Users are not frequently updated and we are already getting distributed events when they are updated. So, normally we don't need to query remote service.