Adding support for some new options:

• --event-id: Allow adding not only admin users but also voters to a specific auth-event.
• --metadata-lookup: By default, voters are found looking up the username, but you can apply this to use some userdata.metadata field instead.
• --update-only: Only will apply user updates, never create a new user, failing if any user is not found.
• --create-only: Only will create previously inexistant users, failing if an user is found.
• --dry-run: If enabled, the script will apply no change, listing the users to be updated/created instead.
• Generates a random username for new users if no username is provided.
• Setting the email and permissions of users is now optional.
• It allows setting some user metadata and children_event_id_list.