async function connectUserHandler(user, workspaceId, callback) {
  user.workspaceId = workspaceId;
  const positionUpdate = {
    workspaceId: workspaceId,
    position: {
      type: null,
      blockId: null,
      fieldName: null,
    },
  };
  await updatePositionHandler(user, positionUpdate, callback);
}
Handler for a connectUser message. Attach the workspaceId to the user and
add the user to the users table.
@param {!Object} user The user connecting.
@param {string} workspaceId The workspaceId for the connecting user.
@param {!Function} callback The callback passed in by WorkspaceClient to
receive acknowledgement of the success of the connection.
@public