Interopability With GCS for S3 QRep

[Amogh-Bharadwaj]

Support for using GCS buckets in S3 QRep

The S3 Peer now looks like:

CREATE PEER s3_gcs_interop_peer FROM S3 WITH
(
    url = 's3://<gcs_bucket_name>/<prefix>',
    access_key_id = '<access_key_id>',
    secret_access_key = '<secret>',
    region = 'auto' -- preferable for GCS,
    endpoint = 'https://storage.googleapis.com' -- must for GCS
);

Note that everything apart from url here is an optional field. If you leave any/all of the other fields out, they will be picked up from the docker-compose.yml file.

• Set the Access Key ID and Secret to your GCS HMAC keys. Click here for more information
  
• Set the region to auto for automatically detecting region based on bucket location
• Set the endpoint to https://storage.googleapis.com

The conditions mentioned here still hold - ensure the GCS bucket you specify above exists already.

You can also set the AWS environment variables in docker-compose.yml

Fixes #501