feat(core): Add support n8n Webhook Proxy Service support

[janober]

Summary

Adds support for a Webhook Proxy service which queues requests until they can be forwarded to the n8n instance.

For it to work two environment variables have to be set: N8N_WEBHOOK_PROXY_URL and N8N_DEPLOYMENT_TYPE

For example:

N8N_WEBHOOK_PROXY_URL="https://username.proxy-service.n8n.cloud/webhook"
N8N_DEPLOYMENT_TYPE=cloud

Can then be enabled on the Webhook-Node:

Related Linear tickets, Github issues, and Community forum posts

Review / Merge checklist

• PR title and summary are descriptive. (conventions)
• Docs updated or follow-up ticket created.
• Tests included.
• PR Labeled with release/backport (if the PR is an urgent fix that needs to be backported)

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1 out of 2 committers have signed the CLA.

✅ csuermann
❌ Jan Oberhauser

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