Add FUTURENET networkPassphrase

[esteblock]

Hello,
I am supporting the @soroban-react library, and for the @soroban-react/chains package I would like to do

import * as SorobanClient from "soroban-client";
export const futurenet : WalletChain = 
  {
    id: "public",
    name: "Futurenet",
    networkPassphrase: SorobanClient.Networks.FUTURENET,
  }

However SorobanClient.Networks.FUTURENET does not exist here

js-stellar-base/types/index.d.ts

Line 220 in afaacb5

export enum Networks {

I think it would be good to add it as Futurenet is important for Soroban development

[Shaptic]

Oh wow you're right, though it's on the Networks object itself in the source code lol

[Shaptic]

Wait no, this is set in the soroban branch:

https://github.com/stellar/js-stellar-base/blob/soroban/types/index.d.ts#L241-L247

I opened #654 to fix the jsdocs, though.