* refactor: create log.Infof and log.Warnf
* refactor: review DNS providers.
- use one `http.Client` by provider instead of one client by request
- use the same receiver name `d` for all `DNSProvider`
- use `http.MethodXXX`
* refactor: logger init.
* Add otc provider.
* Added tests for provider otc.
* Format dns_providers
* fix getZoneId
* Add for tests for provider otc.
* Add proxy to transport in otc provider.
* Use DefaultTransport in otc provider.
* Make loginRequest private in provider otc.
* better error handling in provider otc.
* add more tests for provider otc.
