Support JSON output for Shelley tip query command

[intricate]

At the moment, the output of this command looks like this:

$ cardano-cli shelley query tip --testnet-magic 42
Tip (SlotNo {unSlotNo = 57}) (ShelleyHash {unShelleyHash = HashHeader {unHashHeader = 5820355fd1b83b8e71191f135366ae3c07d7408dcd54329e219cead4bb0bf15f875d}}) (BlockNo {unBlockNo = 2})

However, JSON might look nicer:

{
    "blockNo": 2,
    "headerHash": "5820355fd1b83b8e71191f135366ae3c07d7408dcd54329e219cead4bb0bf15f875d",
    "slotNo": 57
}