Add integration tests for storage credential refreshers

[adutra]

Each major object storage platform has its credentials refresher:

• org.apache.iceberg.aws.s3.VendedCredentialsProvider
• org.apache.iceberg.gcp.gcs.OAuth2RefreshCredentialsHandler
• org.apache.iceberg.azure.adlsv2.VendedAdlsCredentialProvider

All of them have internal AuthManagers because they need to contact the REST catalog. Therefore, we should have integration tests that exercise them.