First boot cloud-init setup for a raspberry pi 3 ubuntu bionic arm64 image passing your SSH key and WIFI settings

cloud-init.sample

#cloud-config
ssh_pwauth: false
chpasswd: { expire: False }
ssh_authorized_keys:
  - "${SSH_KEY_CONTENTS}"
packages:
 - iw
 - wireless-tools
write_files:
  - content: |
      network:
        version: 2
        renderer: networkd
        wifis:
          wlan0:
            dhcp4: yes
            dhcp6: no
            access-points:
              "${SSID}":
               password: "${SSID_PASSWORD}"
    path: /etc/netplan/90-cloud-init-wifi-setup.yaml
runcmd:
  - netplan apply