Add ability to write read/write grant data files via S3

[rpoet-jh]

What?
This PR added ability to read spring Resources from s3 if enabled: eclipse-pass/pass-support#95. This is so we could read the policy.properties file from an s3 bucket.

Now we should extend grant loader to be able to read and write grant data and grant_update_timestamps from an s3 bucket if configured. Currently, read and writing has to be done using a file system.

Why?
Being able to use s3 for reading/writing grant data files would simplify the aws infrastructure and deployment.

How?
Use Spring Cloud AWS library.

Acceptance Criteria
Able to run grant loader passing s3 urls for grant data files, and have grant loader update grant_update_timestamps in s3 bucket.