Add Region Configuration to S3 Client Setup

[elmiomar]

This PR fixes an issue where the S3 client initialization fails due to a missing region.

Changes

• Added the region property to the application.yml configuration file.

cloud:
  aws:
    region: us-east-1

• Set a default value for the region variable used in the getAmazonS3() method.

@Value("${cloud.aws.region:us-east-1}")
String region;

• Set service port to 0 (random) in unit tests to prevent conflicts with the actual service running on port 8083.

Testing

• Unit tests pass.
• Verified that the application starts successfully using oar-docker.