Praefect: same storage name can't be used for different virtual storages

In order to exclude usage of Datastore struct as not actual anymore migration to replication queue is node and set of virtual storages is provided from outside in time of creation of replication manager.

Part of: #2613 (closed)

This change is initial step on the way of the removal of the datastore.Datastore, internal/praefect/models package, also cleaning up of the internal/praefect/config/config.Config struct from node setting and removal of the MemoryDatastore struct. Those are must not be used anymore because there is already a replacement for them implemented by nodes.NewManager.
Current implementation of datastore.Datastore also doesn't support same names of storages for different virtuals that could lead to weird issues.