Samples: Bluetooth: HR: Remove use of ISO config for IPC

When compiling with sysbuild and IPC the samples would use the
nrf5340_cpunet_iso-bt_ll_sw_split.conf config file, which was
incompatible with the sample's host configuration.

Instead of using the ISO configuration file, define a hci_ipc
overlay in each sample with the necessary configurations
that support all host configurations.

This commit also updates the sample.yaml files to split
configurations for single- and multicore builds, as what
needs to be configured for each type is different.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>