Add time remaining notification frequency after threshold is reached #451

Is your feature request related to a problem? Please describe.
Currently, Client shows a time remaining notification at a frequency set in server. After the time warning threshold is reached, this changes to every minute, but that frequency is not set in server.

Describe the solution you'd like
Add a setting to customize time remaining notification frequency after the warning threshold has been reached. Default value should be 1 minute to mimic current behavior.

Describe alternatives you've considered
Client could continue to send notifications at the same frequency as before the threshold is reached, but this may create confusion in users who assume the notification can be ignored. Libraries may also want to have more frequent notifications as the session gets closer to expiring.

Additional context
This will require changes in client to implement as well