Add DefaultAzureCredential Authentication Option

[kometaku]

I'm using Roo Code on an Azure VM. Right now, it only supports authentication with an API key, but I’d love to see an option to authenticate using the managed identity assigned to the VM instead of the API key.

Having this option would save us the hassle of managing API keys and improve security as well.

I think this PR could be helpful:
cline#2862

Thanks for considering my request! I really appreciate it!