We should provide a configuration option for how long the device config backups should be retained.

May be we can use period format here: PnYnMnD , ex: 1 yr - P1Y

https://docs.oracle.com/javase/8/docs/api/java/time/Period.html

Any configs older than configured time should be deleted.

whenever we successfully update a config, just get all the configs where lastCreated < ( current time - period)

If it is the only config for that specific interface, don't delete.

if it is more than one and this config is not the latest config, delete