Altering JSON configuration breaks the Kea instance

The issue was found by @andrei during 1.19 sanity checks: https://mattermost.isc.org/isc/pl/fi9kgr9arfr7mcr8kidernw36e

Performing any operation that alters the Kea configuration (i.e., editing subnets, shared networks, host reservations, or global parameters) breaks the Kea instance if Kea has a database configured (e.g., lease database, hosts database, or config backend database) and the retry-on-startup parameter is set in this database settings. The problem affects all Kea versions from 2.5.5 to 2.7.4.