registry.cern.ch/monit has been configured so all tags are immutable
hence this is not necessary anymore.

The agreement is that if a custom remote write is configured and the
local fluent-bit forward is not enabled then the users will have a
green field labels-wise and the k8s_cluster_name label won't be
enforced.

Before the patch:

λ python3 -m linkcheckmd -v docs/*
__main__.py: error: unrecognized arguments: ./docs/metrics.md ./docs/values.md

If "rules:" is present and no rules are evaluated true then the job is
not added to the pipeline. The current configuration was correctly
omitting the jobs in tags however there was nothing configuring them
to run otherwise (!). This commit fixes that. On a tag the first rule
will be evaluated true and, thanks to "when: never", the job won't be
added as expected, ignoring the rest.