🌱 Add dependabot + standard CI workflows

[clubanderson]

Summary

Adds dependabot.yml for automated dependency updates and standard CI caller workflows:

• ci-signed-commits.yaml — Enforce DCO sign-off on all PRs
• check-typos.yaml — Automated typo detection
• md-link-check.yml — Markdown link validation
• non-main-gatekeeper.yml — Prevent direct commits to main
• stale.yaml / unstale.yaml — Stale issue management
• prow-github.yml / prow-pr-automerge.yml / prow-pr-remove-lgtm.yml — Prow integration

Part of event readiness initiative for llm-d ecosystem.

Test plan

• Verify dependabot PRs appear within 24 hours
• Verify CI workflows trigger on a test PR

[Copilot]

Pull request overview

This PR adds a Dependabot configuration file to automate GitHub Actions dependency updates. This is part of a proactive "event readiness initiative for llm-d ecosystem" to ensure automated dependency management is in place before workflows are added.

Changes:

• Adds .github/dependabot.yml configuration for automated GitHub Actions dependency updates with weekly checks

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[clubanderson]

👋 @chcost @smarterclayton PTAL — this adds standard governance workflows (typo checker, link checker, upstream dependency monitor) via GitHub Agentic Workflows. Ready for review.

[clubanderson]

👋 @smarterclayton @jimcadden PTAL — adds dependabot and standard CI governance workflows (signed commits, agentic workflows, Prow integration). Ready for review.

[clubanderson]

👋 @chcost @jimcadden PTAL — adds dependabot and standard CI governance workflows (signed commits, agentic workflows, Prow integration). Ready for review.

[praveingk]

@clubanderson I have added the go-template in another template, which adds these files too. Can you please check and let me know. This PR can be closed, if everything has been added. Thanks.