How can non-admin users connect to Wi-Fi networks?
Your configuration is correct, but local policy files should be placed inside /etc/polkit-1/localauthority/50-local.d/ and the file extension must be .pkla.
To solve your problem:
sudo mv /etc/polkit-1/localauthority.conf.d/52-wifi-management.conf /etc/polkit-1/localauthority/50-local.d/52-wifi-management.pkla