Supported multiple aliases for environment variables.

[yoavkatz]

In my view, there is a need for a common utility in unitxt, that allows specifying multiple environment variable names and ensuring either only one is set, or all the values are consistent.

This is because there are different conventions for name that exists.

unitxt.os_utils.get_env(“[”AZURE_OPENAI_API_KEY”,”OPENAI_API_KEY”])