Registration Token Refresh (#431 : Rotate registration access token)

Registration Token are to be refreshed when they reach their lifetime.
An OP wide configuration specifies the validity duration of the registration tokens. On each read/update call (client), the token is validated for its lifetime. If the (JWT.issueDate + lifeTime) < currentTime, a new registration token is issued.
Perhaps a better approach would be to add a created_ts in the access_tokens and use that for validity comparisons but that has been avoided to keep the data model as is.