Address improvements to buckets configurations

[petreze]

There are some further requirements that need to be met before the final implementation of cloud bucket uploader. This issue is created to unblock dependent work on bucket configurations and track the progress for the following requirements that are left:

• Use JSON for both bucket-configs.json and bucket-credentials.json files
• Use PBJ library to deserialize those files into java classes
• Remove watcher of credentials file

A continuation of the work done here