bgpd:add local_es_df_preference into l2vpn-evpn es json output

bgpd:add local_es_df_preference into l2vpn-evpn es json output

Added "Local ES DF preference" into bgp l2vpn evpn es json output.

 - show bgp l2vpn evpn es <es-id> json
 - show  bgp l2vpn evpn es detail json

Before Fix:-
```
cumulus@torm-11:mgmt:~$ sudo vtysh -c "show bgp l2vpn evpn es
03:44:38:39:ff:ff:01:00:00:01 json"
{
  "esi":"03:44:38:39:ff:ff:01:00:00:01",
  "rd":"27.0.0.21:15",
  "type":[
    "local",
    "remote"
  ],
  "vteps":[
    {
      "vtep_ip":"27.0.0.22",
      "flags":[
        "esr",
        "active"
      ],
      "dfPreference":32767,
      "dfAlgorithm":32767
    },
    {
      "vtep_ip":"27.0.0.23",
      "flags":[
        "esr",
        "active"
      ],
      "dfPreference":32767,
      "dfAlgorithm":32767
    }
  ],
  "vniCount":10,
  "flags":[
    "up",
    "advertiseEVI"
  ],
  "originator_ip":"27.0.0.21",
  "remoteVniCount":10,
  "vrfCount":3,
  "macipPathCount":33,
  "macipGlobalPathCount":132,
  "inconsistentVniVtepCount":0,
  "fragments":[
    {
      "rd":"27.0.0.21:15",
      "eviCount":10
    }
  ]
}
cumulus@torm-11:mgmt:~$
```

After Fix:-
```
cumulus@torm-11:mgmt:~$
cumulus@torm-11:mgmt:~$ sudo vtysh -c "show bgp l2vpn evpn es
03:44:38:39:ff:ff:01:00:00:01 json"
{
  "esi":"03:44:38:39:ff:ff:01:00:00:01",
  "rd":"27.0.0.21:4",
  "type":[
    "local",
    "remote"
  ],
  "vteps":[
    {
      "vtep_ip":"27.0.0.22",
      "flags":[
        "esr",
        "active"
      ],
      "dfPreference":32767,
      "dfAlgorithm":32767
    },
    {
      "vtep_ip":"27.0.0.23",
      "flags":[
        "esr",
        "active"
      ],
      "dfPreference":32767,
      "dfAlgorithm":32767
    }
  ],
  "vniCount":10,
  "flags":[
    "advertiseEVI"
  ],
  "originator_ip":"27.0.0.21",
  "remoteVniCount":10,
  "vrfCount":3,
  "macipPathCount":33,
  "macipGlobalPathCount":132,
  "inconsistentVniVtepCount":0,
  "localEsDfPreference":50000, ====> Added Local ES DF preference
  "fragments":[
    {
      "rd":"27.0.0.21:4",
      "eviCount":10
    }
  ]
}
cumulus@torm-11:mgmt:~$
```

Ticket:#3411906

Issue:3411906

Testing: UT done

Signed-off-by: Sindhu Parvathi Gopinathan's <sgopinathan@nvidia.com>