feat: add GoCD pipeline for auto-deploy on push to master

[BYK]

Summary

Adds GoCD pipeline templates following the seer pattern for auto-deploy on push to master.

What's added

• gocd/templates/orbital.jsonnet — pipedream config with auto_deploy: true, materials watching sentry-orbital master, US-only deploy (exclude_regions for all non-US regions)
• gocd/templates/pipelines/orbital.libsonnet — 2-stage pipeline: check GH Actions → deploy
• gocd/templates/bash/check-github.sh — verifies 'Build and smoke test' job passed for the commit
• gocd/templates/bash/deploy.sh — k8s-deploy with ghcr.io/getsentry/sentry-orbital:${GO_REVISION_ORBITAL_REPO}
• gocd/templates/jsonnetfile.json + lock — gocd-jsonnet v2.19.0

Deploy flow

push to master
  → GH Actions builds & pushes :nightly + :sha to GHCR
  → GoCD detects new commit on master (auto_deploy: true)
  → checks stage: waits for 'Build and smoke test' GH Actions job to pass
  → deploy-primary stage: k8s-deploy with image tagged by commit SHA

Companion PRs

• devinfra-deployment-service: update orbital-k8s deploy-config to point at sentry-orbital repo (PR forthcoming)
• ops: remove the old orbital-k8s.jsonnet + GH Actions workflow (PR forthcoming)

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