`ignore: true/false`

Description

With manual actions, we want to be able to make them block or not. We're re-using the existing allow_failure mechanism to achieve this, but the name of that key doesn't really make sense since a blocked manual actions isn't really a failure, it's just not a success. We need to rename this key and deprecate the existing one.

Proposal

Create new .gitlab-ci.yml keyword for ignore, which can be true or false which has the same functionality as allow_failure, which will be now deprecated. Internally it may be an "alias".

Links / references