drivers: wifi: esp32: connect to highest signal AP

The station-mode channel scan method is currently set to WIFI_FAST_SCAN
which ignores the signal strength and connects to the first channel found
which may result in poor WiFi bandwidth.

Change the scan mode to scan all channels and connect to the channel with
the highest RSSI.

Fixes #84488

Signed-off-by: Eric Holmberg <eric.holmberg@northriversystems.co.nz>