Move OTP input from entity to config field

[ulope]

Is your feature request related to a problem? Please describe.
The Volvo API seems to semi regularly require a new OTP code.
Currently this has to be submitted by changing a text entity's value which is quite unusual and not easy to remember (since this happens very infrequently).

Describe the solution you'd like
Please move the OTP code input to a config field so it's possible to find intuitively in the UI.

Describe alternatives you've considered
Detect that an OTP code is needed and ask for it via a notification (I don't know enough about HA internals to know if this is easily possible)

Additional context
n/a