Configure Dependabot

[vil02]

The actions/setup-java is out of date in:
https://github.com/OpenElements/hedera-enterprise/blob/aeefb188744e2e132d6b4820bf186ae6bae972ea/.github/workflows/maven.yml#L27

This is a good opportunity to configure dependabot for this repository to keep github actions up to date because we would be able to verify immediately the setup. The basic config could look like this:

---
version: 2
updates:
  - package-ecosystem: "github-actions"
    directory: "/"
    schedule:
      interval: "weekly"
...

[vil02]

It works:

• Bump actions/setup-java from 3 to 4 #57