DNS Azure should support Private DNS Zone

The dns_azure.sh currently only supports Public DNS Zones, by using the /dnszones/ api path. This is documented here: https://learn.microsoft.com/en-us/rest/api/dns/record-sets/create-or-update?view=rest-dns-2018-05-01&tabs=HTTP

By changing this parameter to "/privatednszones/", we can ensure that the DNS Zone is not a publicly accessible one. https://learn.microsoft.com/en-us/rest/api/dns/privatedns/record-sets/create-or-update?view=rest-dns-privatedns-2018-09-01&tabs=HTTP

Open `dns_azure.sh` and locate where the Azure DNS API path for record-set operations is assembled with `/dnszones/`. Use the linked Azure docs to confirm the equivalent private endpoint shape, then update the relevant path segment to `/privatednszones/`. There is no test file named in the issue, so validate by running the Azure DNS provider flow in this repo and checking the request path it uses. Done means DNS updates are sent to Private DNS Zones instead of public DNS zone endpoints.

Scritto dal modello di indicizzazione a partire dal testo della issue.