Add authentication support

[nodiaque]

Hello,

Newer device started to use a new protocol and now require an authentication to be used. In python-kasa, we can either set KASA_USERNAME and KASA_PASSWORD so it's used globally or specify --username and --password on the command line to specify it.

Exemple is KS240 device that require it.

Thank you

[flavio-fernandes]

Hi @nodiaque! You are right, I can see now in the library that there is a credentials attribute:

Ref: https://python-kasa.readthedocs.io/en/latest/smartdevice.html#kasa.DeviceConfig

credentials=Credentials("myusername", "mypassword"),

I think that can be integrated into mqtt2kasa for sure. I am currently out of cycles for doing that, but would love to play with it in the future. Thank you for creating this issue.