* 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.
* Adding output of which envvars are missing in Cloudflare dns provider
* go fmt, duh
* Fixing & adding test(s)
* Adding azure missing env vars checking
* Fixing test
* Doh, fixing up expected output
