Make dynu updates more efficient

[tronikos]

I see you first fetch https://ipv4.text.wtfismyip.com to get the IP address and then you call the v2 API.
This is unnecessary. Instead you could just use https://www.dynu.com/DynamicDNS/IP-Update-Protocol

Because you don't provide pre-built containers, see #24, I removed your addon and setup the let's encrypt addon for the certificate and the following rest sensor:

rest:
  # https://www.dynu.com/DynamicDNS/IP-Update-Protocol
  - resource: https://api.dynu.com/nic/update?hostname=mydomain.freeddns.org&password=sha256ofmypassword
    scan_interval: 600
    sensor:
      - name: "Dynu nic update response"
        value_template: "{{ value }}"

Edit: I moved them to secrets.yaml and I now have:

rest:
  # https://www.dynu.com/DynamicDNS/IP-Update-Protocol
  - resource: https://api.dynu.com/nic/update
    params:
      hostname: !secret dynu_hostname
      password: !secret dynu_password
    scan_interval: 600
    sensor:
      - name: "Dynu nic update response"
        value_template: "{{ value }}"