Prometheus relabeling should decide which snmp-exporter module to use

[vonneudeck]

For the baremetal metrics the service discovery file gives that information via __param_module, but it shouldn’t.
Instead the Prometheus should make that decision during relabeling based on information the service discovery gives via labels.
The reasoning behind that is, that the service discovery should be reusable for other setups and for scenarios that have nothing to do with the snmp-exporter.