Add automatic version updates for github actions with dependabot

[iemejia]

Why:

We can include the dependabot configuration for github actions version updates as part of the templates so downstream keep their projects CI updated.

What's being changed:

Add a dependabot file (we require still to manually activate dependabot on the template repo settings).

Check off the following:

• [x] For workflow changes, I have verified the Actions workflows function as expected.
• [ ] For content changes, I have reviewed the style guide.

[iemejia]

PTAL again @heiskr