luci-app-ddns: rework with new ddns changes

This commit rework the app with the new ddns changes. DDns services are now stored in a dedicated list and the service specific data is stored in a dedicated json. This json can both preinstalled with a companion package or be downloaded on demand. The new app now check if the script is present and give a button to install it if not present in the system.
The app now will search for all the available service in the services directory and optionally if present will include in the list the service not installed from a static list. Special service that use a separate script (for example cloudflare-v4) will install directly in the services directory and will be included automatically.
The app now reset the ddns rule settings on service change.
Also rework the app to drop any global function and rework the function to use more default way to get data.

Signed-off-by: Ansuel Smith <ansuelsmth@gmail.com>