Dependabot configuration

As a Github user I (desperately) want to reduce the signal to noise ratio in my Github notifications so I don't miss important things.

For projects using the copier template, I currently ignore dependabot notifications for Github actions and dependencies pinned by the template (e.g. `pydata-sphinx-theme>`). As maintainers we should publish template updates with well-tested versions of those.

However that doesn't stop the notifications from cluttering my inbox. Can we configure dependabot to ignore those particular dependencies?

It would be ideal if dependabot could actually open PRs with template updates, but that doesn't seem to be a high priority (https://github.com/dependabot/dependabot-core/issues/4410). As an alternative we have played with [renovate](https://docs.renovatebot.com/) which does support copier, but we had [a few issues with that too](https://github.com/renovatebot/renovate/discussions/35310).