samples: Bluetooth: peripheral_hr minimal configuration update

Updated peripheral_hr sample to use separate Zephyr
Controller overlay for minimal configuration.

For bbc_microbit:
Memory region         Used Size  Region Size  %age Used
           FLASH:       96268 B       256 KB     36.72%
             RAM:       16296 B        16 KB     99.46%
        IDT_LIST:          0 GB        32 KB      0.00%

For nrf54l15dk/nrf54l15/cpuapp:
Memory region         Used Size  Region Size  %age Used
           FLASH:       95012 B      1428 KB      6.50%
             RAM:       17744 B       188 KB      9.22%
        IDT_LIST:          0 GB        32 KB      0.00%

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>