samples: wifi: shell: Use the new overlay file for SAP

The overlay file for SAP has additional parameters and fine tuning than
just enable of the feature.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>

samples/wifi/shell/sample.yaml

@@ -218,7 +218,7 @@ tests:
     tags: ci_build_superset
   sample.nrf7002.ap:
     build_only: true
-    extra_args: CONFIG_WPA_SUPP_AP=y CONFIG_NRF700X_AP_MODE=y
+    extra_args: OVERLAY_CONFIG=overlay-sap.conf
     integration_platforms:
       - nrf7002dk_nrf5340_cpuapp
     platform_allow: nrf7002dk_nrf5340_cpuapp