fix(cloud): repoint 8 dead cloud.google.com doc links

[pucedoteth]

Nine link occurrences across six skills return 404 on Google's current docs host. They sit in the "External Resources" / "Resources" sections these skills point an agent at, so an agent following them lands on a 404.

dead path	replacement
kubernetes-engine/docs/how-to/rollout-sequencing	kubernetes-engine/docs/concepts/about-rollout-sequencing
load-balancing/docs/overview	load-balancing/docs/load-balancing-overview
kubernetes-engine/docs/how-to/secret-manager ×2	secret-manager/docs/secret-manager-managed-csi-component
binary-authorization/docs/getting-started-gke	binary-authorization/docs/setting-up
kubernetes-engine/docs/concepts/sandbox	kubernetes-engine/docs/concepts/sandbox-pods
kubernetes-engine/docs/how-to/pod-security-standards	kubernetes-engine/docs/how-to/podsecurityadmission
bigtable/docs/reference/sql	bigtable/docs/googlesql-overview
alloydb/docs/reference/	alloydb/docs/reference/rest

Each replacement was checked for a 200 and for a page title matching the existing link text — e.g. secret-manager-managed-csi-component renders as "Use Secret Manager add-on with Google Kubernetes Engine", which covers both the "Secret Manager Add-on for GKE" and "Google Secret Manager CSI Driver" link texts, and binary-authorization/docs/setting-up renders as "Set up for GKE". After the change all 89 cloud.google.com links under skills/ resolve.

Only link targets changed; no link text, prose, or code was touched.

Two notes:

• I swept all 837 external URLs under skills/ and plugins/. The only other failures were ~15 registry.terraform.io URLs, which are not broken — that host returns "Content not available in your region" for every path from my location, including its own root. I left those alone.
• I see CONTRIBUTING says external PRs aren't accepted. Happy to close this and refile as an issue if you prefer — the table above is the whole report, so nothing is lost either way.

Unrelated finding

skills/cloud/agent-platform-alert-configuration/scripts/analyze_traffic_test.py fails for anyone outside Google: it reads mock data from agent-platform-alert-configuration/_internal, which is not in the repo, not gitignored, and not a submodule, so all 12 of its cases error with FileNotFoundError. The other 13 Python test files pass. I did not touch it because the fix could be either publishing the fixtures or dropping the test, which is your call — happy to file it separately.

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[pucedoteth]

Rebased onto current main and narrowed to the one link that is still broken.

Eight of the nine links this PR originally repointed have since been fixed upstream. The remaining one is in skills/cloud/bigtable-basics/SKILL.md:

• https://cloud.google.com/bigtable/docs/reference/sql returns 404
• https://cloud.google.com/bigtable/docs/googlesql-overview returns 200 and is the GoogleSQL for Bigtable overview

I verified both with a request just now, and confirmed the dead link is still present at line 115 on main.

The PR is now a single-line change and no longer conflicts.

[kweinmeister]

Thank you for flagging these broken links, @pucedoteth! We will be adding link-checking in regression tests soon. This is very helpful for the time being.