sysbuild: introduce Kconfig setting for controlling HCI IPC inclusion

Follow-up: #64704

Introducing NET_CORE_IMAGE_HCI_IPC Kconfig setting to control inclusion
of HCI IPC image when building through sysbuild.

This allows users with custom netcore applications to avoid inclusion
of the default HCI IPC image.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>