Returns a list of users the specified user ID is following.

public func getFollowing(_ userId: User.ID,
                           fields: Set<User.Field> = [],
                           expansions: [User.Expansions] = [],
                           paginationToken: String? = nil,
                           maxResults: Int = 100
  )

Equivalent to GET /2/users/:id/following.

• userId: The user ID whose following you would like to retreive.
• fields: Any additional fields to include on returned objects
• expansions: Objects and their corresponding fields that should be expanded in the includes property
• paginationToken: When iterating over pages of results, you can pass in the nextToken from the previously-returned value to get the next page of results
• maxResults: The maximum number of results to fetch.

A Twitter API response object containing an array of User structs and any pinned tweets in the includes property