how to define types for runtimeConfig keys?

runtimeConfig: {
    public: {
      //-> this can be of type 'apple' | 'banana' | 'cherry'
      fruit: 'apple',
    }
  }

runtimeConfig: {
    public: {
      //-> this can be of type 'apple' | 'banana' | 'cherry'
      fruit: 'apple',
    }
  }