Ignore non-metrics notifications in PrometheusFileDriver

The PrometheusFileDriver is registered as an oslo.messaging notification driver and therefore receives every notification ironic emits, not just sensor data. Versioned notifications such as NodeSetPowerStatePayload fell through to the file-writing path, where the node identifier (node_name/node_uuid/hostname) is absent from the versioned object payload, causing:

TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

The driver now only processes metrics notifications and ignores everything else. Metrics notifications are the conductor event type ‘ironic.metrics’ and the node sensor event types, which ironic builds as ‘hardware.{node.driver}.metrics’. The node event type is matched by pattern rather than an explicit list because the middle segment is the node’s hardware type and can be any value registered in the deployment, so an explicit list would silently drop sensor data for hardware types such as ilo or irmc.

Node notifications for hardware types without a dedicated parser keep their previous behaviour of exporting only the header timestamp metric. As a defensive measure, payloads lacking a usable identifier are now skipped with a warning instead of crashing.