Implement `IFormattable` converter

[Marvin-Brouwer]

Is your feature request related to a problem? Please describe. -

Describe the solution you'd like Implement IFormattable converter as counterpart of the IParsable<T> converter. This one is available for older versions though.

By default it should format to G and you should be able to override if you like.

Describe alternatives you've considered -

Additional context

227

https://learn.microsoft.com/en-us/dotnet/api/system.iformattable?view=net-7.0

[Marvin-Brouwer]

This will be the first OOTB Serialize only converter

[Marvin-Brouwer]

• [x] Don't forget to add an item to the readme's