docs: add guide for reaching a private GCP resource from a deployed task

docs: add guide for reaching a private GCP resource from a deployed task

New how-to under Guides & examples showing how a deployed task can reach
a private-IP-only GCP resource (Postgres, managed Cloud SQL, ClickHouse)
using a build extension, a userspace Tailscale or WireGuard tunnel, and
a local SOCKS5 proxy, with no changes to Trigger.dev. Covers subnet
routing to managed Cloud SQL, cold-start tuning, self-hosting the
control plane with Headscale, and pricing.

Mono-RevId: 8207a71b44134567b1640997fc496dedf3c6e167

Author: ericallam

docs/docs.json

@@ -579,6 +579,7 @@
               "guides/examples/libreoffice-pdf-conversion",
               "guides/examples/open-ai-with-retrying",
               "guides/examples/pdf-to-image",
+              "guides/examples/private-gcp-resource",
               "guides/examples/puppeteer",
               "guides/examples/react-pdf",
               "guides/examples/react-email",