Allow token authentication for 'hook' switch component (#6922)

The Hook switch component currently uses username/password to get a token
from the Hook web app to use for subsequent requests. This adds an option
to specify the token directly in config.

Makes the 'password' and 'token' options mutually exclusive since
otherwise one would have to take precedence, and it seems worth
preventing people from filling their config with passwords that don't
even need to be there.