Support inputs for `rules` and `needs`

This change set adds rules and needs inputs for all job templates where it makes sense. We cannot just add it to all of them because null is not supported as a (default) value, see Backend: Implement support for "null" value to ... (gitlab-org/gitlab#440468).

It also adds _rules inputs to the opinionated job templates.

The only breaking change is in the job-templates template where we do not define any rules.

Refs #75 (closed) #51 (closed)