Implement most popular caddy-dns provider plugins

[Monviech]

Current build:

https://caddyserver.com/api/download?os=freebsd&arch=amd64&p=github.com%2Fcaddy-dns%2Fcloudflare&p=github.com%2Fcaddy-dns%2Fduckdns&p=github.com%2Fcaddy-dns%2Fdigitalocean&p=github.com%2Fcaddy-dns%2Fdnspod&p=github.com%2Fcaddy-dns%2Fhetzner&p=github.com%2Fcaddy-dns%2Fgodaddy&p=github.com%2Fcaddy-dns%2Fgandi&p=github.com%2Fcaddy-dns%2Fvultr&p=github.com%2Fcaddy-dns%2Fionos&idempotency=29198543194239

If a new DNS Provider has been added, you have to remove and reinstall caddy to get the latest binary. Just updating is not enough. Don't worry, your configuration won't be deleted.

DNS Providers that use the standard "dns provider apikey" in the Caddyfile

• [x] - Cloudflare is already implemented in Version 1.1.4r
• [x] - duckdns - Yes
• [x] - digitalocean - Yes
• [x] - dnspod - Yes
• [x] - hetzner - Yes
• [x] - godaddy - Yes
• [x] - gandi - Yes
• [x] - vultr - Yes
• [x] - ionos - Yes (not that popular but I need this)

DNS Providers who need bells and whistles:

route53 - Needs too many custom fields. Only if there's high demand. alidns - Needs too many custom fields. Only if there's high demand. googleclouddns - Needs too many custom fields. Only if there's high demand. azure - Needs too many custom fields. Only if there's high demand.

[Monviech]

https://github.com/Monviech/os-caddy-plugin/pull/47

[Monviech]

Closing because I won't add more for a while. New requests will get new issues.