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.

This patch forces Helm to abort if kubernetes.clusterName is not set
when *.fluentbit.enabled = true.

Moreover, if Prometheus remote write is enabled and
`metrics.prometheus.server.remoteWrite.username` and
`metrics.prometheus.server.remoteWrite.password` are not set the chart
will fail to install now.

With this patch the chart will fail to install if either tenant.name
or tenant.password are not set if they're necessary, example:

```
λ helm -n monitoring diff upgrade kubernetes-monitoring . -f values.yaml -f ibarrien.yaml
Error: Failed to render chart: exit status 1: Error: execution error at (cern-it-monitoring-kubernetes/templates/fluentbit-metrics/configmap.yaml:22:13): Tenand password is required
```

If no fluentbit forwarding is configured, i.e.:

```yaml
metrics:
  fluentbit:
    enabled: false

logs:
  fluentbit:
    enabled: false
```

then the chart installs fine as they're note required in that case.

This should prevent the following from happening in the MONIT clusters
that push metrics directly from Prometheus to MoM without any
Fluentbit in between:

ts=2025-02-14T11:37:32.111Z caller=dedupe.go:112 component=remote
level=warn remote_name=6c01d0
url=http://it-monit-metrics-fluentbit:8080/api/prom/push msg="Failed
to send batch, retrying" err="Post
\"http://it-monit-metrics-fluentbit:8080/api/prom/push\": dial tcp:
lookup it-monit-metrics-fluentbit on 10.254.0.10:53: no such host"