Added to auth command

[thibauult]

The openhue auth command is used to retrieve the hue-application-key.

🕙 22:32:07 ❯ go run . auth -h

Authenticate to retrieve the Hue Application Key. Requires to go and press the button on the bridge

Usage:
  openhue-cli auth [flags]

Flags:
  -b, --bridge string       Bridge IP (example '192.168.1.23')
  -d, --devicetype string   Device identifier (default "tpensec-mbp")
  -k, --generateclientkey   Generate the client key (default true)
  -h, --help                help for auth