For secondary interfaces, it's better to allow more configurable
indexing for pods enrichment. For some network types, pods might be identified by their MAC
address advertized in the network-status annotations, while in others it
can be by IP, by interface name, or any combination of those.

This PR makes it all configurable in that way (example):

```bash
secondaryNetworks:
- name: my-network
  index:
    mac: true
    ip: true
```

More than one network can be configured that way.

Additionally, a new metric is added to track which indexer is used for
every enrichment hit: promql:
`sum(rate(netobserv_secondary_network_indexer_hit[1m])) by (kind,
network, error)`

This metric can also report errors and unexpected multiple matches

…t network