Bluetooth: Samples: periodical_adv_rps: Added sync wait delay

Problem:
on cyw208xx devices i see sometime `Timed out while synchronizing`
error in samples periodical_adv_rps/periodical_sync_rps.

log:
<err> bt_scan: Could not lookup connection handle from PAST
<err> bt_scan: Unknown handle 0x0000 for periodic advertising report
Timed out while synchronizing
...

After investigation i can confirm, the sync was created successful,
but in application (periodical_sync_rsp) terminated the sync when the
connection is not valid.

periodical_adv_rps doesn't have any mechanism to wait for sync and after
gatt write (subevent, response_slot information) it immediately
performs disconnection.

Solution:
Added sync wait delay before make disconnection, to ensure sync
is established before disconnection.

Signed-off-by: Nazar Palamar <nazar.palamar@infineon.com>