Create identity

Before #2 (closed), an identity must be created (https://duniter.org/wiki/duniter-v2/runtime-calls/#create-identity-0). create_identity(owner_key)

Contrary to Duniter v1 where the user declares his name before getting the first certification, for the moment in Duniter v2, an identity must be created first, which also triggers a certification.

See https://git.duniter.org/clients/cesium-grp/cesium2s/-/blob/6fe34ad1f2b5effa0783f008cde765a7b951a190/src/interfaces/augment-api-tx.ts#L473 for the API.