Allow properties from the .properties file to be set via environment variables.

Having to generate this properties file for each environment is not at all 12 factor app. It would be nice if setting STREAM_NAME and others via environment variables overrode properties file values. Kind of like auth works for the sdk.

No file or test is named in the issue. Trace how the Ruby client loads the .properties file and how SDK authentication reads environment variables, then verify that documented environment variables take precedence and add focused coverage for the override behavior.

Written by the indexing model from the issue text.