Unsafe yaml deserialization in NVFlare

NVFLARE, versions prior to 2.1.2, contains a vulnerability in its utils module, where YAML files are loaded via yaml.load() instead of yaml.safe_load(). The deserialization of Untrusted Data, may allow an unprivileged network attacker to cause Remote Code Execution, Denial Of Service, and Impact to both Confidentiality and Integrity.