Configure Renovate (#268)

Welcome to [Renovate](https://github.com/renovatebot/renovate)! This is an onboarding PR to help you understand and configure settings before regular Pull Requests begin.

🚦 To activate Renovate, merge this Pull Request. To disable Renovate, simply close this Pull Request unmerged.

---
### Detected Package Files

 * `.gitea/workflows/dev.yaml` (github-actions)
 * `.gitea/workflows/prod.yaml` (github-actions)
 * `go.mod` (gomod)

### What to Expect

It looks like your repository dependencies are already up-to-date and no Pull Requests will be necessary right away.

---

❓ Got questions? Check out Renovate's [Docs](https://docs.renovatebot.com/), particularly the Getting Started section.
If you need any further assistance then you can also [request help here](https://github.com/renovatebot/renovate/discussions).

---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).

<!--renovate-config-hash:94693a990c975907e7f13da3309b9d56ba02b3983519b41786edf5cf031e457c-->

Reviewed-on: #268
Co-authored-by: Renovate Bot <renovate-bot@git.cantorgymnasium.de>
Co-committed-by: Renovate Bot <renovate-bot@git.cantorgymnasium.de>

renovate.json

@@ -0,0 +1,3 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json"
+}