ci: add dependabot for gitsubmodules and github-actions

[kunish]

Background

Use dependabot for auto-updating gitsubmodules and github-actions instead

See the example resulting PR at here

Checklist

• [x] The Pull Request has been fully tested
• [x] There's an entry in the CHANGELOGS
• [ ] There is a user-facing docs PR against https://github.com/daeuniverse/dae-wing

Full Changelogs

• ci: add dependabot for gitsubmodules and github-actions

Issue Reference

NA

Test Result

NA