Do not show non-nullable errors when errors are manually rendered from controller

[povilasjurcys]

This could be done by:

• adding custom context key like context[:rendered_errors] = true
• overriding GraphQL::Schema#type_error logic to:

   def type_error(type_error, context)
     return nil if type_error.is_a?(GraphQL::InvalidNullError) && context[:rendered_errors]
     super()
   end

Bonus points:
Make it easier to add hooks before_type_error and after_type_error for adding logger logic or so

     def type_error(type_error, context)
       before_type_error&.call(type_error, context)
       super().tap { |result| after_type_error&.call(type_error, context, result) }
     end