Drop `metrics` and `metrics-exporter-prometheus` in favour of
`prometheus`, and completely reimplement how metrics are done.
This gives me much more control over them, and also makes process-based
metrics available as a bonus.
Signed-off-by: Gergely Nagy <me@gergo.csillger.hu>
Lifted out the label construction code into its dedicated function, so
it can be reused to add labels to `iocaine_garbage_served` too. The
required information is at hand at that point, so the cost of doing this
is minimal.
Changelog & Grafana dashboard adjusted accordingly.
Signed-off-by: Gergely Nagy <me@gergo.csillger.hu>
