DNS caching on IGEL OS#457

Implement DNS caching on IGEL OS (for example through the systemd-resolved as a local caching resolver) and a supported mechanism for activating/configuring the behavior through UMS profiles, in order to reduce unnecessary query load on DNS infrastructure.

Running Citrix Workplace App on IGEL OS 12 endpoints we observed that each device generates a very high volume of DNS queries - in the hundreds per hour. This is understood to be by design, as the Citrix Workspace App repeatedly resolves certain hostnames during normal operation.

We have compared this behaviour against Windows endpoints running Citrix Workspace App, where OS-level DNS caching (via the Windows DNS Client service) reduces the number of outgoing queries to fewer than 10 per client per hour - a significant improvement.