add Dependabot

[sullis]

Description

enable Dependabot version 2 for dependency management

https://github.blog/2020-06-01-keep-all-your-packages-up-to-date-with-dependabot/

Before submitting a PR:

We love getting PRs, but we hate asking people for the same basic changes every time.

• Push your changes to a branch other than master. Create your PR from that branch.
• Add JavaDocs and other comments
• Write tests that run and pass in CI. See CONTRIBUTING.md for details on how to capture snapshot data.
• Run mvn clean compile locally. This may reformat your code, commit those changes.
• Run mvn -D enable-ci clean install site locally. If this command doesn't succeed, your change will not pass CI.

When creating a PR:

• Fill in the "Description" above.
• Enable "Allow edits from maintainers".