vtysh, lib: fix 'show ip[v6] prefix-list ... json' formatting by moving it to vtysh

vtysh, lib: fix 'show ip[v6] prefix-list ... json' formatting by moving it to vtysh

Json output is not valid for 'show ip[v6] prefix-list ... json' commands,
as it goes through all the running daemons and for each one it calls
'vty_show_prefix_list' creating a new json object. To aggreagate the output
and create a valid json that can be parsed, the commands were moved to vtysh.

Before:
{
  "ZEBRA":{
    "DEFAULT":{
      "addressFamily":"IPv4",
      "entries":[
        {
          "sequenceNumber":10,
          "type":"permit",
          "prefix":"0.0.0.0/0"
        }
      ]
    }
  }
}
{
  "OSPF":{
    "DEFAULT":{
      "addressFamily":"IPv4",
      "entries":[
        {
          "sequenceNumber":10,
          "type":"permit",
          "prefix":"0.0.0.0/0"
        }
      ]
    }
  }
}
{
  "BGP":{
    "DEFAULT":{
      "addressFamily":"IPv4",
      "entries":[
        {
          "sequenceNumber":10,
          "type":"permit",
          "prefix":"0.0.0.0/0"
        }
      ]
    }
  }
}

After:
{"zebra":{
  "DEFAULT":{
    "addressFamily":"IPv4",
    "entries":[
      {
        "sequenceNumber":10,
        "type":"permit",
        "prefix":"0.0.0.0/0"
      }
    ]
  }
}
,"ospfd":{
  "DEFAULT":{
    "addressFamily":"IPv4",
    "entries":[
      {
        "sequenceNumber":10,
        "type":"permit",
        "prefix":"0.0.0.0/0"
      }
    ]
  }
}
,"bgpd":{
  "DEFAULT":{
    "addressFamily":"IPv4",
    "entries":[
      {
        "sequenceNumber":10,
        "type":"permit",
        "prefix":"0.0.0.0/0"
      }
    ]
  }
}
}

Signed-off-by: Piotr Suchy <piotrsuchy@proton.me>