Add support for WPA2 in wifi AP mode

[Grant]

I'm trying to use a raspberry pi as an access point, but it appears that for access points the only (non-enterprise) security supported by netplan is WPA, not more secure/modern standards like WPA2 (or WPA3).

Here is my simple netplan config file in /etc/netplan/50-cloud-init.yaml:

version: 2
renderer: NetworkManager

network:
 ethernets:
  eth0:
   dhcp4: true
   optional: true

 wifis:
  wlan0:
   optional: true
   access-points:
    "my_wifi_ssid":
      mode: ap
      auth:
       key-management: psk
       password: "my_wifi_password"

This works, but only protects the network with WPA(v1). Currently, the available key management options are "none", "psk", "eap", and "802.1x". What would be awesome is expanding the "psk" option to include the higher-security modes, for example "psk-wpa", "psk-wpa2", etc. wpa-supplicant already supports this so I imagine this would only add a minimal amount of logic.

Other details:
Hardware: Raspberry Pi 4
Software: Ubuntu 18.04.4 LTS 64-bit (from https://ubuntu.com/download/raspberry-pi)