Since the labels are dynamically created for each metric, the "code" label
of the ST_F_HRSP_1XX field is missing. To fix the bug, this metric is
handled in the same way the other ST_F_HRSP_* field are. We only take care
to dump the metric header only once.
This bug was introduced by the commit 5a2f93873 ("MEDIUM:
contrib/prometheus-exporter: Use dynamic labels instead of static ones"). No
backport needed.
32ef48e984