Access files from gs and s3 buckets anonymously.

[gsaluja9]

Currently, the way we instantiate s3 and gcloud storage client assume that credentials will be provisioned in the environment or use profile.
But there is a rare case of needing to access Read only public storage buckets.

That should be supported in case of downloading files anonymously.

[ali-asadpoor]

There are two types of links for objects:

1. https://storage.googleapis.com/ad-demos-datasets/workflows_streaming/train/stuff_train2017_pixelmaps/000000000009.png
2. https://storage.cloud.google.com/ad-demos-datasets/workflows_streaming/train/stuff_train2017_pixelmaps/000000000009.png

I think the first type should work out of the box.