Is your feature request related to a problem or challenge? Please describe what you are trying to do.

Currently the object_store crate only supports obtaining credentials using a provided service account, it would be beneficial if it could also optionally obtain credentials from its environment. This would be consistent with the behaviour of the aws and azure implementations, and avoids requiring users to handle sensitive long-term service account credentials.

Describe the solution you'd like

If no service account is specified, it should fallback to trying to get credentials from a metadata endpoint.

This is documented here

Describe alternatives you've considered

Additional context