text: Title: Output a warning when an unknown config option is present
  Body: ## Problem
  
  <!-- A clear and concise description of what the problem is. Ex. I'm always frustrated when [...] -->
  
  Someone may misspell a config option and not realise until they don't get the behaviour that they want. This would be confusing
  
  ## Suggested solution
  
  <!-- A clear and concise description of what you want to happen. -->
  
  We can avoid the whole confusion mentioned above by outputting a warning indicating that the option is unknown.
  
  We shouldn't raise an error as it isn't really a fatal error and shouldn't block someone from deploying or using the client.