* Add file transfer over RPC
* Snapshot transfer implementation
* Allow snapshot creation only for MAIN instances
* Replica and main can have replication clients
* Use only snapshots and WALs that are from the Main storage
* Add flush lock and expose buffer
* Add fstat for file size and TryFlushing method
* Use lseek for size
Co-authored-by: Antonio Andelic <antonio.andelic@memgraph.io>