Enable all the danger defaults

What does this MR do?

Enable all the danger defaults

Dangerfiles are located by default under the danger/**/*. So this change moves dangerfiles there to simplify configuration.

By calling import_dangerfiles instead of importing single files separately, we'll also inherit all the Dangerbot rules. Including the reviewer roulette: https://gitlab.com/gitlab-org/ruby/gems/gitlab-dangerfiles#rules

Closes gitlab-org/distribution/team-tasks#1417 (closed)

Related issues

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion

Required

• Merge Request Title, and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Integration tests added to GitLab QA
• The impact any change in container size has should be evaluated
• New dependencies are managed with dependencies.io