gitlab-ci.d/base: Mark jobs as interruptible by default

gitlab-ci.d/base: Mark jobs as interruptible by default

When handling pull requests in the staging branch, it often happens
that one of the job fails due to a problem, so that the pull request
can't be merged. Peter/Richard/Stefan then informs the sender of the
pull request and continues by pushing the next pending pull request
from another subsystem maintainer. Now the problem is that there might
still be lots of other running jobs in the pipeline of the first pull
request, eating up precious CI minutes though the pipeline is not
needed anymore. We can avoid this by marking the jobs as "interruptible".
With this setting, the jobs from previous pipelines are automatically
terminated when pushing a new one. If someone does not like this auto-
matic termination, it can still be disabled in the settings of the
repository. See this URL for details:

 https://docs.gitlab.com/ee/ci/yaml/index.html#interruptible

Message-Id: <20230223191343.1064274-1-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>