func NewBundle(jd json.RawMessage) (credentials.Bundle, func(), error)
NewBundle returns a credentials.Bundle which implements mTLS Credentials in xDS Bootstrap File. It delegates certificate loading to a file_watcher provider if either client certificates or server root CA is specified. The second return value is a close func that should be called when the caller no longer needs this bundle. See gRFC A65: github.com/grpc/proposal/blob/master/A65-xds-mtls-creds-in-bootstrap.md