Change which token is sent to n8n

[lisajulia]

Change the behavior described in https://github.com/cap-java/cds-feature-n8n/blob/main/docs/adr-webhook-authentication.md
-> Do not send the token X-N8N-API-KEY for all requests to N8N but make this configurable via a user provided service (see cap-js/n8n#33)