.github: Add a dependabot config

[mrueg]

Adds a Dependabot configuration that checks for golang and github actions dependency updates

[fujita]

This notifies the version update of all the packages?

[mrueg]

It will create a PR if there's a new version of a golang dependency released or there's a new version of a used github action published.

[fujita]

I would like to update a package only when it has a security issue or such.

[mrueg]

Ah understood. Then this is likely not what you want for this repository.

Closing then :)