Add DDNS support (#324)

* feat: add ddns updater framework

Note: no functionality implemented yet

* feat: add webhook ddns provider

* feat: update dashboard template

* fix: check nil and cron task string

* fix: webhook string formated with unexcepted param

* fix: webhook header split error

* feat: cloudflare ddns provider

* refract: move ddns update trigger into ReportSystemInfo

* lang: update other languages text

* fix: clear codes and logics

* fix: move update ddns to goroutine to avoid blocking

* fix: clear unused codes

* fix: update timestamp to prevent cache

script/config.yaml

@@ -12,3 +12,13 @@ site:
   brand: "nz_site_title"
   cookiename: "nezha-dashboard" #浏览器 Cookie 字段名，可不改
   theme: "default"
+ddns:
+  enable: false
+  provider: "webhook"
+  accessid: ""
+  accesssecret: ""
+  webhookmethod: ""
+  webhookurl: ""
+  webhookrequestbody: ""
+  webhookheaders: ""
+  maxretries: 3