snapshot restore: default to `SNAPSHOT_DATA_PATH=data` when isn't set

[Andrey Arapov]

Set SNAPSHOT_DATA_PATH=data always by default when SNAPSHOT_DATA_PATH is not set.

Otherwise the node will just either start syncing / or get stuck (due to version incompatibility) from/at the height=1: 12:50PM INF executed block height=1 module=state num_invalid_txs=0 num_valid_txs=0 server=node.

Refs.
https://discord.com/channels/747885925232672829/1082763714060623923/1097896337669881916