[keyserver][lib][web] set up anonymous connection with tunnelbroker on keyserver and handle DEVICE_LIST_UPDATE_SUCCESS

Summary:
the keyserver needs to be able to establish an anonymous connection with tunnelbroker in order to receive the message indicating that it has been added to the user's device list.
once it has been added, it needs to auth with the identity service (next diff).

this diff just establishes the anonymous connection and parses the DEVICE_LIST_UPDATE_SUCCESS message from tunnelbroker.

Test Plan:

const { primaryDeviceID: receivedPrimaryDeviceID, userID } =
  qrCodeAuthMessage;
console.log(receivedPrimaryDeviceID, userID);

added the above lines to tunnelbroker-socket.js and confirmed that the user ID and primaryDeviceID were received

Reviewers: bartek, kamil

Reviewed By: bartek

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D12146