Enable OCI Instance Principal Authentication

Problem: Running scoutsuite against OCI configurations is currently difficult in the context of CI/CD. Instance principal authentication is not supported, bucket queries are currently broken, and KMS queries also return errors.

Solution: I'd like to fix the behavior for querying KMS for OCI and enable Instance Principal Authentication using a -i flag for scoutsuite oci

Alternatives: Using a config file in CI/CD is possible, but it's somewhat painstaking. We could also skip all Bucket and KMS queries, but that removes half the scan.