Set UseOutputFormatters to true by default

[mauroservienti]

This is a breaking change. We should allow setting UseOutputFormatters to false merely for backward compatibility. Consider also obsoleting the configuration option and removing it in v3.

Using output formatters require additional settings (https://github.com/ServiceComposer/ServiceComposer.AspNetCore/blob/master/docs/output-formatters-serialization.md). Before turning this on by default, it must be evaluated how to check if the prerequisites are met or how to add them automatically