Use correct DSN protocols in gateway

[teor2345]

In a recent refactor, I used the wrong gateway node config. The protocol version is missing a /subspace/2/ prefix, and the piece fetching protocols weren't enabled.

As part of this change, I also added a fallback from the farmer cache (L2) to archival storage (L1).

In the current implementation, all the DSN connections fail:

$ subspace-node run --chain mainnet --tmp
$ RUST_LOG=subspace=debug,subspace_networking=info,subspace_networking::utils::piece_provider=debug,info subspace-gateway run
$ websocat --jsonrpc ws://127.0.0.1:9955 | jq .
subspace_fetchObject {"mappings": {"v0": {"objects": [["0000000000000000000000000000000000000000000000000000000000000000", 0, 0]]}}}

2024-11-07T22:28:00.703640Z DEBUG subspace_networking::node_runner: Peer has different protocol version, banning temporarily local_peer_id=12D3KooWB9bHyw97AcEzCGDabL1dgaFU4K2q5a3DopQU9F4jaWs8 peer_id=12D3KooW9sMSK3i9pkPQaQJgWkVVeN7gzrgHD6kAGQKuycqUAWVY local_protocol_version=66455a580aabff303720aa83adbe6c44502922251c03ba73686d5245da9e21bd peer_protocol_version=/subspace/2/66455a580aabff303720aa83adbe6c44502922251c03ba73686d5245da9e21bd

{
  "jsonrpc": "2.0",
  "id": 1,
  "error": {
    "code": 9001,
    "message": "ObjectFetcherError(PieceNotFound { piece_index: PieceIndex(0) })"
  }
}

After these fixes, it works:

subspace_fetchObject {"mappings": {"v0": {"objects": [["0000000000000000000000000000000000000000000000000000000000000000", 0, 0]]}}}
{
  "jsonrpc": "2.0",
  "id": 1,
  "error": {
    "code": 9001,
    "message": "InvalidObjectHash { mapping_hash: 0000000000000000000000000000000000000000000000000000000000000000, data_hash: af1349b9f5f9a1a6a0404dea36dcc9499bcb25c9adc112b7cc9a93cae41f3262 }"
  }
}
subspace_fetchObject {"mappings": {"v0": {"objects": [["af1349b9f5f9a1a6a0404dea36dcc9499bcb25c9adc112b7cc9a93cae41f3262", 0, 0]]}}}
{
  "jsonrpc": "2.0",
  "id": 2,
  "result": [
    ""
  ]
}

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