Enable dependabot and scala-steward

This can wait until after the release of daffodil-sbt 1.0.0.

How to enable dependabot:
- Copy dependabot.yml from daffodil/.github to daffodil-sbt/.github, remove "docker", commit, and open a pull request. Once that PR is merged, [@dependabot](https://github.com/dependabot/dependabot-core) will check periodically for version updates.

How to enable scala-steward:
- Open a pull request that adds `apache/daffodil-sbt` to [repos-github.md](https://github.com/VirtusLab/scala-steward-repos/blob/main/repos-github.md) ([edit](https://github.com/VirtusLab/scala-steward-repos/edit/main/repos-github.md)). Once that PR is merged, [@scala-steward](https://github.com/scala-steward) will check periodically for version updates.

[Optional] How to enable code scanning:
- Configure one of the 74 [code scanning](https://github.com/apache/daffodil-sbt/actions/new?category=security&query=code+scanning) workflows offered by GitHub.

After daffodil-sbt 1.0.0 is released, compare daffodil/.github/dependabot.yml with the target repository and review the requested entry in scala-steward's repos-github.md. The work is complete when the Dependabot configuration and Scala Steward repository request are submitted and merged; code scanning is explicitly optional.

Written by the indexing model from the issue text.