Add DuckDNS certbot plugin

Uses https://github.com/infinityofspace/certbot_dns_duckdns certbot plugin to implement DuckDNS DNS challenge in order to obtain Wildcard certificates.

Requires that the user inserts his duckDNS token in "Credentials File Content" input box.

global/certbot-dns-plugins.js

@@ -322,4 +322,13 @@ certbot_dns_transip:dns_transip_key_file = /etc/letsencrypt/transip-rsa.key`,
 certbot_dns_acmedns:dns_acmedns_registration_file = /data/acme-registration.json`,
 		full_plugin_name: 'certbot-dns-acmedns:dns-acmedns',
 	},
+	//####################################################//
+	duckdns: {
+		display_name:    'DuckDNS',
+		package_name:    'certbot-dns-duckdns',
+		package_version: '0.5',
+		dependencies:    '',
+		credentials:     `<DUCKDNS_TOKEN>`,
+		full_plugin_name: 'certbot-dns-duckdns:dns-duckdns',
+	},
 };