wpa_supplicant / iwd: add "wlan" provide to openrc service

This allows services that need to run before iwd or wpa_supplicant (e.g. for enabling/configuring wireless hardware) to have an explicit dependency on these services.

Using before net isn't always appropriate in these situations since iwd also has before net, so there's a chance that other things that need to run before iwd might not run before iwd starts. But iwd needs to be started before net so that e.g., NetworkManager can use it. So with this approach, we can make sure iwd/wpa_supplicant are started after these other services by adding before wlan to these other services.

Some context here: https://gitlab.com/postmarketOS/pmaports/-/merge_requests/4564#note_1676995163