Sidenote, uv doesn't support SSL_CERT_DIR directly but we should probably add explicit support so as its properly supported by rustls-native-certs as of a few months ago.

Originally posted by @samypr100 in #16412

For validation of ssl_cert_dir_exists, I'd use the approach from rustls-native-certs, validating each path and issuing a warning for paths that don't exists similar to ssl_cert_file_exists logic.