get Signed Time
Provides signed date time. Signed date time should be fetched from Tedee API every time that sdk request it.
Parameters
callback
A function to be called with the fetched signed date-time. it will looks like this: signedTimeProvider?.getSignedTime { setSignedTime(it) } where 'setSignedTime' is a method that applies the signed date-time to send a command to the lock.