Autobuild: Add Github Action for dependency update PRs

**Describe the task**

We have several external dependencies which are version-locked for reproducibility and security. We should regularly check those for updates. A Github Action scheduled job (cron-style) could do that. It could automatically submit a PR with the suggested update.

- [ ] Github Actions (`uses: `) #2778
- [ ] Pinned dependencies in the build process (aqt, Qt, JACK, jom, NSIS) #2777
- [ ] Android SDK/NDK/Commandlinetools)
- [ ] Check #2345 wrt completeness
- [ ] Submodules (liboboe)
- [ ] Add automated update to pylint (inclusion here closes https://github.com/jamulussoftware/jamulus/issues/3056)

Solutions to look into:
- dependabot
- https://github.com/apps/renovate