include timestamp also part of sidechain transaction object

sidechain transaction object today does not have a timestamp.

[{
    "id": "1.39.2",
    "sidechain": "hive",
    "object_id": "1.37.1",
    "transaction": "057BD3A6D64DC5784B6101020B736F6E2D6163636F756E74096163636F756E743032007D0000000000000354424400000000000000",
    "signers": [{
        "son_id": "1.33.0",
        "weight": 1,
        "signing_key": "TEST8TCQFzyYDp3DPgWZ24261fMPSCzXxVyoF3miWeTj6JTi2DZdrL",
        "sidechain_public_keys": [[
            "bitcoin",
            "03456772301e221026269d3095ab5cb623fc239835b583ae4632f99a15107ef275"
          ],[
            "peerplays",
            "TEST8TCQFzyYDp3DPgWZ24261fMPSCzXxVyoF3miWeTj6JTi2DZdrL"
          ],[
            "hive",
            "sonaccount01"
          ]
        ]
      },{
        "son_id": "1.33.1",
        "weight": 1,
        "signing_key": "TEST82qv1LKFvwVKD9pg5JQf6qqwLcoeqUniQjWJ3wKTodyWa7gHUs",
        "sidechain_public_keys": [[
            "bitcoin",
            "02d67c26cf20153fe7625ca1454222d3b3aeb53b122d8a0f7d32a3dd4b2c2016f4"
          ],[
            "peerplays",
            "TEST82qv1LKFvwVKD9pg5JQf6qqwLcoeqUniQjWJ3wKTodyWa7gHUs"
          ],[
            "hive",
            "sonaccount02"
          ]
        ]
      },{
        "son_id": "1.33.2",
        "weight": 1,
        "signing_key": "TEST6xdp7MrEPnaNK9GuF3KTeTizgGN6JC5nPmxx81higFepSZ8N7r",
        "sidechain_public_keys": [[
            "bitcoin",
            "025f7cfda933516fd590c5a34ad4a68e3143b6f4155a64b3aab2c55fb851150f61"
          ],[
            "peerplays",
            "TEST6xdp7MrEPnaNK9GuF3KTeTizgGN6JC5nPmxx81higFepSZ8N7r"
          ],[
            "hive",
            "sonaccount03"
          ]
        ]
      },{
        "son_id": "1.33.3",
        "weight": 1,
        "signing_key": "TEST55j32Up75gHCxJBPN18vEytL9anDgEVFtsaCii38keGQG71X22",
        "sidechain_public_keys": [[
            "bitcoin",
            "0228155bb1ddcd11c7f14a2752565178023aa963f84ea6b6a052bddebad6fe9866"
          ],[
            "peerplays",
            "TEST55j32Up75gHCxJBPN18vEytL9anDgEVFtsaCii38keGQG71X22"
          ],[
            "hive",
            "sonaccount04"
          ]
        ]
      },{
        "son_id": "1.33.4",
        "weight": 1,
        "signing_key": "TEST68bX5bB16GkEAig6w2WTh9NbM9nHa66CemnDRx2njRY9bbWXhU",
        "sidechain_public_keys": [[
            "bitcoin",
            "037500441cfb4484da377073459511823b344f1ef0d46bac1efd4c7c466746f666"
          ],[
            "peerplays",
            "TEST68bX5bB16GkEAig6w2WTh9NbM9nHa66CemnDRx2njRY9bbWXhU"
          ],[
            "hive",
            "sonaccount05"
          ]
        ]
      },{
        "son_id": "1.33.5",
        "weight": 1,
        "signing_key": "TEST7mtTyM2rD18xDTtLTxWhq6W6zFgAgPFu9KHSFNsfWJXZNT8Wc8",
        "sidechain_public_keys": [[
            "bitcoin",
            "02ef0d79bfdb99ab0be674b1d5d06c24debd74bffdc28d466633d6668cc281cccf"
          ],[
            "peerplays",
            "TEST7mtTyM2rD18xDTtLTxWhq6W6zFgAgPFu9KHSFNsfWJXZNT8Wc8"
          ],[
            "hive",
            "sonaccount06"
          ]
        ]
      },{
        "son_id": "1.33.6",
        "weight": 1,
        "signing_key": "TEST7RMDnipLkFaQ4vtDyVvgyCedRoxyT9JWpAoM9mrE7rwVSyezoB",
        "sidechain_public_keys": [[
            "bitcoin",
            "0317941e4219548682fb8d8e172f0a8ce4d83ce21272435c85d598558c8e060b7f"
          ],[
            "peerplays",
            "TEST7RMDnipLkFaQ4vtDyVvgyCedRoxyT9JWpAoM9mrE7rwVSyezoB"
          ],[
            "hive",
            "sonaccount07"
          ]
        ]
      }
    ],
    "signatures": [[
        "1.33.0",
        "20551CEF0090F92CE6D709296EA206C6230F2C509C2B1F1C21CD6A7F1613AE2D2574D7EE95D9C3EF88D93EB5556A10A5BCBBB3C907F65B6BEEE828599971362524"
      ],[
        "1.33.1",
        "203EA6B82F91ECF820B3AEFE5F4FB99E987A14ACEC6652A0533CA1EE1E3E7AC7F1019E448E4D9FBEE4A6731225F8805617676818563D106E9D53F878E1731D1CD5"
      ],[
        "1.33.2",
        "1F6269EF8714EA49538BA35B6100778EDF82EBB0C6648176C28AFDDD338F9D85F74D402229A45B717EC91476F84D42686F64197C3984054EA96352103D3D20AFF5"
      ],[
        "1.33.3",
        "202CC76368EFF91CFC21FECE27389C4616F0406A769EEA00A3B01F5DF16A72928544893D6A961160EC79DB2A8BC36271C6E574E9109F7F14B475F87881911CAB4A"
      ],[
        "1.33.4",
        ""
      ],[
        "1.33.5",
        ""
      ],[
        "1.33.6",
        "1F2BAC21AE109FB4956260371E87B436ED993373562DB710D4012D69BABA46DB134915B51AF6FE7571362C96482CFD78CDD2072E8AA2712B7138D38F2D4474F074"
      ]
    ],
    "sidechain_transaction": "6599b425f82b56746b80b064d3565c4c982e5d09",
    "total_weight": 7,
    "current_weight": 5,
    "threshold": 5,
    "status": "sent"
  }
]