Onboard Renovate using new shared preset

[erikgb]

Without makefile-modules. This project is a bit "special", since it probably serves as a template for people who want to create a new external issuer.

But the dependencies in this project are lagging behind, and we have two open PRs to fix some of this. So there is a need. I also want to use this project to test the new shared preset a bit more.

[Copilot]

Pull Request Overview

This PR onboards Renovate dependency management using a new shared preset configuration, without makefile-modules. The setup enables automated dependency updates for this project which serves as a template for external issuer implementations.

• Adds a GitHub Actions workflow to run Renovate on a daily schedule
• Configures Renovate using a shared preset from cert-manager/renovate-config
• Sets up STS token exchange for secure authentication with Chainguard

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
.github/workflows/renovate.yaml	GitHub Actions workflow for running Renovate daily with STS authentication
.github/renovate.json5	Renovate configuration extending shared cert-manager preset
.github/chainguard/renovate.sts.yaml	STS configuration defining permissions for Renovate operations

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[ThatsMrTalbot]

/lgtm
/approve

[cert-manager-prow]

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