SDK should use local configuration file when no ENV variables are available

Much like kubectl, aws and gcloud-cli, az-cli: env variables are the first source of credentials, but they all fall back to local credentials (using the current configured profile)

No file or test is named in the issue. Start at the SDK's credential handling and compare the existing environment-variable behavior with the requested fallback to local credentials using the current configured profile; done means environment variables remain first, with local credentials used only when they are unavailable.

Written by the indexing model from the issue text.