[TRUNK-17580] Add Google Cloud Build CI provider documentation

[samgutentag]

Summary

• Add new Google Cloud Build CI provider page at flaky-tests/get-started/ci-providers/google-cloud-build.md
• Cover full setup: GCP Secret Manager for Trunk token, Cloud Build GitHub App connection, trigger creation (PR + push), and cloudbuild.yaml configuration
• Document required environment variables (TRIGGER_NAME, PROJECT_ID, BUILD_ID, BRANCH_NAME, _HEAD_BRANCH, _PR_NUMBER) — these must be explicitly passed since Cloud Build does not auto-provide them to build steps
• Include example configurations for both JUnit XML and Bazel BEP uploads
• Add Google Cloud Build to CI Providers index page card grid and summary.md table of contents

Linear tickets

• TRUNK-17580 — Add Google Cloud Build CI provider documentation for Flaky Tests (previous attempt was canceled, this is a fresh PR)
• TRUNK-17525 — Related: CLI flags for non-standard CI usage
• TRUNK-16338 — Related: AgencyAnalytics uploads from Google Cloud Build

Engineering authors

• @dfrankland (Dylan Frankland) — authored analytics-cli PR #1031 (Google Cloud Build env var parsing) and flake-farm PR #17341 (example cloudbuild.yaml)

Context links

• Slack thread (initial request): https://trunk-io.slack.com/archives/C05LX5HB1FZ/p1770229066379849
• Slack thread (Dylan's instructions): https://trunk-io.slack.com/archives/C08AEDGMZNH/p1770770187339799
• analytics-cli PR #1031: add google cloud build envs analytics-cli#1031
• flake-farm PR #17341: add cloudbuild.yaml flake-farm#17341
• analytics-cli release v0.12.5: https://github.com/trunk-io/analytics-cli/releases/tag/0.12.5

Files changed

• flaky-tests/get-started/ci-providers/google-cloud-build.md (new)
• flaky-tests/get-started/ci-providers/README.md (updated card grid)
• summary.md (added ToC entry)

Open questions

1. Google Cloud Build icon: The CI Providers README card grid references google-cloud-build.png as the card cover image. Dylan submitted trunk2 PR #2861 for the UI icon, but a docs-ready PNG for the GitBook card grid needs to be added to .gitbook/assets/. Without this image, the card will render without a cover.
2. Trunk CLI launcher vs analytics-cli binary: The draft notes used trunk-analytics-cli directly. This PR uses the ./trunk flakytests upload pattern consistent with all other CI provider docs. Confirm this is correct for Google Cloud Build (the Trunk launcher should auto-detect the platform the same way).

Test plan

• Check GitBook preview renders correctly
• Verify summary.md entry appears in correct alphabetical position
• Verify Google Cloud Build card appears in CI Providers index
• Confirm example cloudbuild.yaml is syntactically valid
• Have @dfrankland review for technical accuracy
• Add google-cloud-build.png icon to .gitbook/assets/

Generated with Claude Code

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