Snapshots - validate that the snapshot is on the same file system

[VanBarbascu]

Context

Snapshots are taken at the epoch boundary to facilitate resharding and state parts generation for state sync.
A snapshot is taken using RocksDB builtin functionality. In the background, it creates hard links to the db at the moment of snapshot.

Problem

The hard links are created as an optimization if the snapshot folder is on the same file system. If the destination is on a different fs, the snapshot will copy the entire db. This operation is not instant and will stall the functionality of the node.

Code pointers

StateSnapshotConfig
get_state_snapshot_base_dir is where we compose the path.

Test steps

• setup a node with neard init
• setup config.json to enable snapshots every epoch.
• run the node and check if the snapshots are taken.
• stop the node
• mount another fs in the folder where the snapshots are taken
• run the node and check if it detects that the snapshot path is on another FS.