Ability to renew aws credentials without application restart

[IskandarovRost]

Not sure about system variables or Java properties, But it seems it could be simply implemented for ~/.aws/credentials.

Environment

• Platform version: 7.2-beta1

Description of the bug or enhancement

• Minimal reproducible example

1. Create ~/.aws/credentials file with some incorrect or outdated AIM keys in [default] profile

2. in app.properties define some existent bucket/region
   do not define credentials there! This will activate default credentials provider

cuba.amazonS3.region = us-west-1
cuba.amazonS3.bucket = cuba-the-best

3. Start the application

4. Open Administration -> External files. And try to upload\download something: ensure it does not work

5. Then correct ~/.aws/credentials
   

6. Open Administration -> External files. And try to upload\download something: check if ot starts working

• Expected behavior
  The credentials are renewed - read from ~/.aws/credentials.

• Actual behavior
  The credentials are renewed only after the application re-start.
  

[soraksh]

Added AmazonS3Manager MBean with refreshS3Client() method. It will refresh S3Client with current properties and credentials will be reloaded from file if needed (note that data from system variables or Java properties won't be reloaded).

[IskandarovRost]

The Bean method could be scheduled.