Decouple the lifecycles SLRP metrics from SLRP itself.

Currently, the lifecycles of SLRP metrics are the same as the SLRP they monitor. This means that if the SLRP fails and is being destructed the metrics will be gone as well. This makes the metrics less useful for operators to monitor SLRP. We should move the StorageLocalResourceProviderProcess::Metrics class outside SLRP.