modules: hostap: Add Kconfig option for debug key material

Add CONFIG_WIFI_NM_WPA_SUPPLICANT_DEBUG_SHOW_KEYS option to control
whether key material (passwords, encryption keys, etc.) is included
in debug output. This is equivalent to the -K command line flag in
wpa_supplicant.

The option:
- Defaults to disabled (n) for security reasons
- Includes clear warning about security risks
- Should only be enabled during development/debugging
- Provides compile-time control over key material logging

This allows developers to enable key material debugging when needed
while maintaining security by default.

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