export missing types from tuf-js pkg

[bdehamer]

Exports the UpdaterOptions and Config types used by the Updater.

Previously, you had to go through some weird contortions to get ahold of the Config type:

const config: ConstructorParameters<typeof Updater>[0]['config'] = {
  fetchTimeout: 5000,
};

Now consumers can simply do:

const config: Config = {
  fetchTimeout: 5000,
};