Allow to omit traits and environment API keys in `dumporganisationdatatolocalfs`

[khvn26]

Symptom: loaddata raises IntegrityError when the target database already contains the same trait or API key.

Root cause: Both models define natural_key() (used during serialisation) but their managers lack get_by_natural_key() (needed during deserialisation). Without it, loaddata always attempts an INSERT rather than an UPDATE, hitting unique constraints.

Fix: To dumporganisationdatatolocalfs CLI management command, add an option to omit traits and environment keys entirely — these updates are not expected to be needed for the air-gapped env use case.