Errors when "upgrading" the app and reading a config that is from an old version

[baruchiro]

When we are working with the config read and write, we are assuming that the loaded config is in the correct schema, because it saved by us or loaded from the default schema.

But if you adding a new Exporter, for example, it will cause an error since the exporter in the config is not nullable, but because it is a new exporter, it does not exist in the existed config.

Also, if you think the app is separated into two parts- one is managing the config, and the second is giving the config to the scraping process, you don't want the user will have to create a full config with all the exporters, just for marking all the exporters as enabled=false.

What I'm saying is that maybe all the config properties on all the levels should be nullable.