This command reads keyfile data from the environment and generates on-disk keyfiles.

This command relies on environment variables which must be set prior to running this command.

1. `GOOGLE_CLOUD_PHP_KEYFILES` is a base64-encoded, json-encoded list of keyfiles to load. For instance, if you only need a single keyfile to run system tests, this environment variable should be the value of `base64_encode(json_encode(['KEYFILE_NAME']))`.
2. `<KEYFILE_NAME>_ENCODED` is a base64-encoded, json-encoded keyfile. There must be one environment variable corresponding to each member of `GOOGLE_CLOUD_PHP_KEYFILES` and it must contain the keyfile in its expected format.