Remove support for Agroal in EAP 8.0 servers; convert subsystem to Domain Controller only

Agroal has never made it to full support and it was deprecated in EAP 7.4. It also lacks some features that datasources subsystem has, like XA transaction support.

There was short discussion on chat wrt this and one mentioned option was to drop Agroal support from EAP 8 now and evaluate re-adding later if there is a demand. We've now discussed this and decided to remove support in EAP 8.0 servers.

The subsystem will be converted to a "model only" stub that an EAP 8 Domain Controller can use to manage EAP 7.4 secondary Host Controllers that have servers using the subsystem.