DD_API_KEY and DD_APP_KEY at call time, which
the plugin previously did not do. Each falls back independently, so one key
may come from a secret while the other stays in the environment.apiKey and appKey are optional, since either can now come from the
environment, and both are declared mutable so rotating a key updates the
target rather than replacing it.DATADOG:: prefix (forma files that import the
Datadog schema need no change).