Goal: Implement a generic `RequiredByKeys<T, K>` which takes two type arguments `T` and `K`. `K` specifies the set of properties of `T` that should be set to required. When `K` is not provided, it should make all properties required just like the normal `Required<T>`. Source challenge: https://github.com/type-challenges/type-challenges/tree/main/questions/02759-medium-requiredbykeys Reference explanation: https://github.com/ghaiklor/type-challenges-solutions/blob/main/en/medium-requiredbykeys.md