feat(terminal): add option to set string token

[rdlabo]

close #335

use native http client for getting a token

(async ()=> {
  /**
   * tokenProviderEndpoint: The URL of your backend to provide a token. Use Post request to get a token.
   */
  await StripeTerminal.initialize({ tokenProviderEndpoint: 'https://example.com/token', isTest: true })
  const { readers } = await StripeTerminal.discoverReaders({
    type: TerminalConnectTypes.TapToPay,
    locationId: "**************",
  });
  await StripeTerminal.connectReader({
    reader: readers[0],
  });
  await StripeTerminal.collect({ paymentIntent: "**************" });
});

set string token

(async ()=> {
  // run before StripeTerminal.initialize
  StripeTerminal.addListener(TerminalEventsEnum.RequestedConnectionToken, async () => {
    const { token } = (await fetch("https://example.com/token")).json();
    StripeTerminal.setConnectionToken({ token });
  });
});
(async ()=> {
  await StripeTerminal.initialize({ isTest: true })
  const { readers } = await StripeTerminal.discoverReaders({
    type: TerminalConnectTypes.TapToPay,
    locationId: "**************",
  });
  await StripeTerminal.connectReader({
    reader: readers[0],
  });
  await StripeTerminal.collect({ paymentIntent: "**************" });
});