Schema fields that start with underscore should be hidden in the API response

[subnetmarco]

In some situations it's very convenient to cache some otherwise long operations inside the datastore in specific private fields, like https://github.com/Mashape/kong/blob/master/kong/plugins/ssl/schema.lua#L27-L29

This is to avoid the "Dogpile Effect" in production, and increase performance.

This fields are currently being displayed in the API response, while they should only be visibile internally. Not sure if we want to use the underscore convention, or have a specific hide = true property for the field.

[thibaultcha]

Sounds good. I'm more in favour of the hide = true than the underscore, just to stay consistent with how fields acquire properties.

[subnetmarco]

@thibaultcha this needs to be implemented in the Admin API right before returning the response, because we still want to have the visibility of the fields when the DAO is being invoked.

[subnetmarco]

Actually hide = true is the wrong property name. Should be internal = true.