Add versioning-strategy: increase

[archanaserver]

This PR adds versioning-strategy: increase to the dependabot.yml configuration. This change is enforce to pin to y-stream, ensuring that dependabot only suggests updates within the existing version constraints.

[evgeni]

Interestingly, https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#versioning-strategy says that bundler doesn't support widen, which would mean that auto (which we have right now) is the same as increase (which is what you're changing to).
But, https://github.com/theforeman/theforeman-rubocop/pull/30/files clearly looks like widen was used.

That said, could you explain a bit more why you'd want to switch to increase?
Wouldn't that mean we never (automatically) notice newer (and possibly more problematic releases) and rely on manual bumps for those?

We could, to avoid blind bumps, set up CI here that runs Rubocop on Foreman and Katello with the (new) constraints from PRs, so we are more confident whether a bump can become problematic (or not)?